It usually takes some minimum in oil also
Yes, defenitely EDM is normally not done in air but in oil
(die-sinker) or (deionized) water (wire edm).
Pay attention if you use oil, it could begin to burn (the spark must
absolutely not happen near the oil-surface but deep submerged). I
would suggest to use water to begin becaus it's harmless...
It is possible to erode also with 80V, but you need to get closer...
(~20 micrometers?).
If you don't want to use more power-supplys you could also build a
step-up converter. Since the spark-gap-voltage is about 20-25V
(depends on electrode and machined material),the best would be to use
a source lower than that voltage.
Diode
-----------Inductor---------| -------------------
__|__ | __|__ | electrode
_____DC source _|/switch _____ C *
| (below 24V) |\ | _____Workpiece
---------------------------------------------------

The switch can be a NPN-bipolar transistor or a mosfet.
If you searches the web for a step-up converte circuit you'll surely
get a more compensible picture as my bad ascii-art...