The 20mm PVC pipe I tried to use for the Fuego Austral dome wasn’t stiff enough to support much weight, let alone wind loading; it supported maybe 10kg above and beyond its own weight at the crossing of three pipes in the center of the six-pointed star dome. It was 1mm thick and cost AR$27 (US$1.80) for three meters. The largest pipes available in the category were 46.8 mm inside diameter, 50.8 mm outside diameter, and are thus 2mm thick: twice the wall thickness, 2.4 times the lever arm, and 2.4 times the perimeter, for a product of 11.5 times stiffer. I’m not absolutely sure, but I think it cost AR$95 for three meters, 3.5 times more cost (and thus 3.3 times more cost-effective at buying stiffness), and would have weighed 4.8 times as much per three meters. 11.5 times stiffer would imply it could carry about 110 kg of load at the center of the dome.
I paid some AR$700 for 26 three-meter lengths of the 20mm pipe. At AR$95 per three-meter length, this would be AR$2470 (US$164). Adding the AR$1450 cost of the 81 square meters of used advertising vinyl we bought to cover it, the total comes to some AR$4000 (US$263). This amount of vinyl is a bit of overkill: only 57 square meters should be necessary, costing only AR$1026. But then, the whole design is kind of overkill.
The longer lever arm means that the roughly 500mm radius of curvature I established in destructive testing in Parque Lezama would be about 1.2 m. This still seems like a pretty tight curve: a 2.4-meter-diameter circle is quite tight compared to the 6-meter diameter of the desired dome. Thicker pipe walls would help more with resilience; spreading the same material over more area would help more with stiffness.
If this amount of pipe encloses a 5-meter-diameter circle of effectively usable floor space, that’s 19.6 square meters of floor space, at a cost of about US$13 per square meter.
A standard 18-panel H18 12-foot hexayurt is 8 feet (2.4 m) on each hexagonal side and 2.4 meters tall at the inside of the wall; I suppose that means it's 2.1 meters from the center to a wall, making its interior consist of six 2.1-meter-height, 2.4-meter-base triangles, for a total of 15.4 square meters of usable floor space. http://www.appropedia.org/Category:Hexayurt_project says it costs “around [US]$300 per unit”. It originally used 1" (25mm) Tuff-R foil-faced polyisocyanurate foam panels, according to http://www.appropedia.org/Hexayurt_playa#Which_Hexayurt.3F, but http://www.appropedia.org/Hexayurt_Safety_Information says that’s a fire risk. Also apparently the necessary four rolls of tape cost like US$150, and FOAMULAR 150 panels of 1" thickness (without even the aluminum facer!) currently costs US$19 at Home Depot, for US$342 total cost for the foam and thus US$490 for the total hexayurt, US$31/m². This is about 2.4× the cost of the dome. (Rmax Thermasheath-3 1-inch 4'×8' R-6 polyisocyanurate panels with aluminum facers cost US$19.25 each at the Emeryville Home Depot, so this is probably actually about the right cost.)
Another interesting comparison is the weight. The dome probably weighs about twice the weight of its vinyl coating, which is, say, 400g/m²; that's 22.8kg of vinyl in the dome, or about 46kg total, or 2.3kg/m² of usable floor. The Thermasheath-3 boards weigh 7 pounds each, according to http://www.homedepot.com/p/Thermasheath-Rmax-Thermasheath-3-1-in-x-4-ft-x-8-ft-R-6-Polyisocyanurate-Rigid-Foam-Insulation-Board-787264/100549260, which works out to 57kg, or about 3.7kg/m² of usable floor.
So, this dome is several times cheaper than a hexayurt and a bit lighter, but it might also be significantly less livable because it provides little to no insulation. A closer comparison might be a plywood hexayurt, which is US$132 for those same 15.4m².
A minimal-cost composite dome covering might consist of Tyvek, Mylar, and bubble wrap. I don’t know if this can get near the cost of AR$18/m² (US$1.20/m²) that we’re paying for used opaque billboard covering, but I suspect so.
http://articulo.mercadolibre.com.ar/MLA-611584214-cinta-de-aluminio-puro-de-30-micrones-ideal-para-aislacion-_JM offers 30-micron aluminum reflecting tape for AR$400 per roll of 45 m × 48 mm, a product of 2.16m².
http://articulo.mercadolibre.com.ar/MLA-612633055-membrana-burbuja-10mm-aluminizada-aislante-termico-_JM is 3.5mm-thick aluminized bubble-wrap membrane for insulating uses for AR$289, 1m × 15m, or AR$19/m². It says “10mm” in the description, but this is misleading; that’s the diameter of the bubbles.
http://articulo.mercadolibre.com.ar/MLA-604333399-aislante-aislacion-termica-para-techos-rollo-x-25-m2-_JM is a roll of 25m² of bubble wrap (polyethylene, I suppose) without an aluminum facing for AR$121, or AR$4.84/m². No thickness is specified, but I suspect 3.5mm.
http://articulo.mercadolibre.com.ar/MLA-612656558-membrana-aislante-espuma-tipo-isolant-tba10-10mm-aluminizada-_JM is a 1m × 20mm roll of 10mm-thick aluminized flexible polyethylene foam for AR$530, or AR$26.50/m².
http://articulo.mercadolibre.com.ar/MLA-614120886-aislante-termico-burbujas-aluminizado-20-m2-_JM is 19.4m² of 3.5mm-thick aluminized bubble wrap for AR$320, or AR$16.50/m². This is probably the best bet so far.
Various space-blanket products on Mercado Libre are about 4m² for about AR$150, or about AR$40/m². It seems like aluminized Mylar ought to be available for less money, but I’m not seeing where.
One of the geodesic domes I saw at Fuego Austral was covered with silage plastic (for covering heaps of grains). This is perfectly opaque and airtight, and it’s white to keep down solar heating of the grain pile. It seems likely to have a lower cost per square meter than other reflective, opaque substances; http://articulo.mercadolibre.com.ar/MLA-614005553-bolsa-para-silo-agrinplex-9x60-f-forraje-segura-_JM is a bag of such plastic of 9 feet diameter and 60 meters of length, “Agrinplex” brand, for AR$7000. (Silobolsa and Siloplast are two other brands.) If we figure that 9 feet diameter means 28 meters of circumference, which is 8.6 meters, that’s 517 m², or AR$13.50/m². If combined with bubble wrap, it might make an adequate dome covering. However, it’s probably not as strong or stiff as Tyvek.
http://articulo.mercadolibre.com.ar/MLA-614441671-tyvek-rollo-130-x-12-m-_JM is a 1.3 m × 12 m roll of Tyvek for AR$479, or AR$30.70/m². This by itself is considerably more expensive than the billboard vinyl it replaces in this use.
http://articulo.mercadolibre.com.ar/MLA-614133525-wichi-roofing-igual-a-tyvek-membrana-hidrofuga-x-m2-_JM is a 1.16 m × 26 m roll of off-brand Tyvek clone (“Wichi” brand) for AR$484, or AR$16/m², about the same cost as the billboard vinyl.
http://articulo.mercadolibre.com.ar/MLA-606787652-tyvek-aislacion-hidrofuga-techo-superior-a-ruberoid-_JM is a 1 m × 30 m roll of Tyvek for AR$1050, or AR$35/m². It gives the weight of the roll as 2.8kg, or 93 g/m². This is something like 20% of the weight of the billboard vinyl (the vendors say 30%, but my tired back says otherwise, although maybe the vinyl was wet or something.) The publication clarifies that it's 100% HDPE and weighs 80.6 g/m² (maybe the other 12g/m² is the cardboard it's wound around) and is 220μm thick.