I have been persuaded into using a fixed 24 volt wart, and a Sepic converter on my board to go programmably from, say, +5 to +75 volts. I'm Spicing that. I'll just have to include some shielding to avoid the switcher getting into the other stuff.
Digikey will custom program one of the programmable XOs to nearly any frequency for around $2 and up.
I can make a big (say, 30 volts p-p) square wave with my little GaN thing, and bandpass that to get a nice sine wave.