If you buy from anyone who knows its rarity nowadays you'll pay 340-360k. Once in a while (once a month or so) someone is selling theirs for 300k+, but that's rare. If you see one being sold for ~320k, buy it for guaranteed profit, or if you desperately want full 512 you might pay 340-350k.
also, 256 ground is more like 40k
and 256 head more like 8k