After spending quite some time with Schaffner 438 it has broken (finally
) and because for repair they want almost what we paid for used one I figured that ESD Simulator would be a nice project for a final year of university. I figured out that 15kV would be maximum voltage that we need but I am having hard time finding relays that have enough voltage rating and are non-bouncing. Currently my only candidate is gigavac G15 but it costs 800+$ 
Are there any cheaper alternatives. Somewhere I read that you can use relays from defibrillator...
Relays with mechanical contacts bounce. The only exception are mercury-wetted types, but those aren't available in HV ratings. In fact, at this voltage you are mostly going to find vacuum relays and they are breathtakingly expensive if purchased new.
Defibrillators operate at 5kV or less, so a single relay from one isn't going to cut the proverbial mustard, and while it is possible - if not entirely kosher - to stack relays in series to increase the voltage rating, you would still need to add RC networks across each one to improve dynamic voltage balancing (that is, to reduce the voltage overstress seen by the first relay to open or the last one to close).
Probably a better approach to producing low-energy 30kV pulses is dumping charge from a capacitor into a small flyback or xenon strobe trigger transformer (or, if you have the available space, an old automotive ignition coil - which is just a flyback transformer).