A 256 field maximum would work better than 200. Normally, tournaments work best with fields of 8, 16, 32, 64, 128, 256, 512, 1024,…
A $300 entry and half as much for a re-buy seems good. The entry amounts would be about the same.
256 players x $300 = $76,800
480 players x $160 = $76,800...