@carsbad. Pure sine wave inverters are not very expensive at all really. I can buy a 1000W unit out of Asia that will produce a fairly accurate sine wave for < $100. They are a dime a dozen on Amazon, Alibaba, etc. At light loads they produce good sine waves. At heavy loads there is some distortion. I even quickly found a DIY link for a 1KW pure sine wave based on old technology. The person built it for <$50 of parts. Probably not much of a market for those big old transformers so they are cheap.
Rhodium is an adequate conductor of electricity for a coating that is 10-20um. You would need very good equipment to measure the resistance of a coating that thin. It is poor because it is very hard.
You can’t install 240 outlets willy nilly. The NEC is written to prevent that. They can only be legally installed to support a device that requires that level of power (not voltage). Those appliances you have have 240V outlets because they require the power that 240V can deliver. It is NEC 210.6 (in complete) that specifies this.