The technology is widespread, you can buy spools of wires and wind your own coils. A spool might still be in the range of 3k$+, probably due to the manufacturing costs of all those single wire strands.

However, as we already know, the superconductivity currently starts only at low temps and I think the wires are limited by a maximum current (max field density?)

If you handle the spool, NEVER lose the beginning of the wire, always fixate it, otherwise there might be a knots after some unspooling, then you might need to buy a new one.

High temperature super conductors is a term of art. It does not mean what it sounds like. They still have to be pretty cold.

I'm not sure what your criteria are, but high-Tc superconductors are used in a bunch of commercial applications. Magnet windings, very high-Q RF filters, and some exotic switching applications. "High temperature" still means liquid-nitrogen cooled but compared to liquid helium that's swelteringly hot.