Voltages upwards of 10 kV can be generated with a simple 555 IC circuit and a DC flyback transformer. I put this one together in a few days during my summer break.

Schematic

D2, D17 and D18 are TVS diodes matched to the specific MOSFET being used for switching, and the 25uH inductor represents the primary of the flyback transformer. Note that the 4 ohm resistor can get rather warm after extended operation.

Pictures

The circuit on protoboard.

Driving an induction coil.