The preferred material for RF coils is LITZ wire (multiple strands, interwoven ) which reduces the impedance considerably and consequentially the losses. The cheapest way though is to use copper tube, which is also more easily obtained. and that works a lot better if it's silver plated.

I remember seeing a quote for replacing a burned out Litz coil at the old GPO site in Rugby - it worked out at four and a half times the cost of putting a coiled copper tube in. The problem is the Q, which is much improved with Litz wire.

A question of horses for courses. And cost. (I have an invoice here from the BBC for a couple of 300 microHenry coils to carry 50A of RF; they wanted £800 for them. (Still in our garage somewhere if anyone needs one!)