you could get a belva 2000, vvme 1500, shark 2500 (if you can find one for around $150) or any of the 1000-1500w amps at 1ohm and they should put out around 600 at 2ohm. just set your gain conservatively.
that way you will have the option to upgrade in the future easily. either get a second and run at 1ohm, or get different subs.
p.s. the vvme doesnt like .5ohm but it will run full out for a solid 10 seconds, then protect then another 10 seconds
the shark seemed to work well at .5ohm
i havnt used my belva yet but it seems like a decent amp
also you can get these amps for between $100-$150 new