I'm afraid so. Capacitor banks often add up to being one of the most expensive parts of a DRSSTC. My coil uses 36 Aerovox RBPS IGBT snubber capacitors (2uF 530VAC each, 18s x 2p) giving me 222nF at 9.54kV. I'm running off 120V mains (170VDC bus) so this was plenty for me. You could probably get away with a similar setup but you'll risk blowing caps. I bought 50 of these capacitors from an online surplus store for $55 including shipping.Oh.
That's going to add up to a lot of caps...
Ouch, $20 a pop? Keep in mind the AC rating is probably about half the DC rating, so you'd need at least 17 of them in series to get the voltage rating you need. Even with the high price of caps for DRSSTCs you shouldn't have to spend $340+. See if you can find someone selling these Aerovox RBPS 2uF 1000VDC (530VAC) caps in bulk:A string of these may work.
Which tool did you use? Generally you need to select your capacitor bank and then tailor your primary coil to match. You'll need to find a balance between the two.My calculations for the tank cap size were done through JavaTC, I take it this is incorrect?
I don't see any information about the capacitor itself. If you can find a datasheet I'd be happy to look it over.