Copper plating is an effective technique for preventing microbial contamination of surfaces; it can also prevent corrosion and contact dermatitis from other metals. US pennies are zinc electroplated with 20 microns of copper; this is sufficient to prevent them from wearing visibly even over the course of decades. The Royal Mint claims that their 25-micron coating is sufficient to give circulating currency a life of 25 to 30 years.
How much would it cost to buy enough copper to copper-plate furniture, plates, doorknobs, silverware, walls, etc.? Let’s suppose that 10 microns is adequate, since we can replate when it wears through after a few years, so each m² of surface is 10 μ(m³) = 10 mℓ. Copper’s density is 8.96g/mℓ, so that’s 0.0896kg/m². At the moment, the price of NYMEX HG contracts — in some sense the wholesale price of copper — is US$2.26 to US$2.30 per pound. That works out to about US$5 per kg, which works out to a copper cost of about US$0.45/m² for this 10-micron plating.
So copper-plating your entire house is going to be dominated by the cost of the plating process, not of the copper itself. The copper itself is a quite affordable cost.
In fact, you might be able to dumpster-dive enough copper to copper-plate every surface in your house. An AWG20 copper wire, suitable for carrying 5 amps, is 0.812 mm in diameter, according to Induction kiln; a meter-long power cord cut off a small discarded appliance might contain two of them, contains just over one cubic centimeter of copper, which is to say 8.96 g — enough to copper-plate a thousand square centimeters, which is quite a bit of silverware and door handles.
Around here, larger chunks of copper and copper alloys are rapidly dumpster-dived by cartoneros, who even break the yokes off discarded CRTs to recover the copper, typically within an hour or two. So finding free copper by the kilogram is not common; nevertheless, I've picked up a discarded microwave oven or two.
As reported in Immersion plating of copper on iron with blue vitriol, it’s feasible to electroplate copper using vinegar and salt, though professional metal finishers are not enthusiastic about “hardware-store chemistry”. A nickel flash (also platable with vinegar and salt) is recommended to get an adherent copper coating on steel, while for chromium-based stainless steel, people on #electronics have told me that copper will adhere directly, while nickel-plating it requires a copper flash. I haven’t tried it yet, but I bought some Argentine 1941 50-centavo pieces made of pure nickel.
The 2001 edition of the ASM Specialty Handbook Copper and Copper Alloys says, on p.133, Figure 4, in the “Copper and Copper Alloy Coatings” chapter, that it is practical to achieve copper deposit thickness of 3 to 3.5 μm per minute with 8–10 amperes per square decimeter with periodic current reversal, at I think 6 volts; as its source it cites “Electroplating Engineering Handbook, Reinhold, 1971, p. 748, 750”. This would provide the desired 10μm thickness in about three minutes at a cost of, say, 9 A/dm² · 100 dm²/m² · 3 minutes · 6 V = 972 kJ/m² ≈ 1MJ/m². That’s about US$0.027/m² for the energy at a retail cost of US$0.10/kWh, which is measurable, but more than an order of magnitude lower than the cost of the copper itself.