Schematics for the simple power oscillators used to drive ultrasonic
cleaners (for cleaning metal parts) can be found at:
Some of the MOSFET's cited are obsolete; you can substitute a 400-volt
or 500-volt part of current manufacture from ST or IR. One candidate
might be STP14N50Z, $3.24 each from Digi-Key.
Warning: voltages exceeding 1 KV at lethal power level can exist in
these circuits at resonance. I won't answer design questions, but
others might. Have fun, be careful.