question regarding a transformer
You could consider an oil burner ignition transformer, such as these, which cost around $40 and are not small. They have a 10kV output winding with center grounded, (the latter which may or may not be acceptable for your application). 



For 600VAC out, the required input voltage would be 7.2V RMS (about 10V peak) and they should work okay at 5Hz with up to  800VAC+ out. 

The usual approach in this frequency range would be to create some high voltage rails (+/- somewhat more than your peak output voltage requirement) and use a high voltage DC-coupled amplifier to drive the crystal. 

In either case, crystal capacitance could cause issues with amplifier stability. The transformer will multiply the output capacitance by about 7000:1 (square of the turns ratio).