If you have to do it now, a 580exII and a 430exII - hopefully used. If you're open, a Nissin Di866mk2 & Di622mk2 (using the 866 as the IR master if you're looking for eTTL). A single 600ex will cost the full amount you're looking to spend. The 580ex and Di866 also support external battery packs if you're looking for faster recycle.
Any ability or interest with dialing in the strobes manually? Lots of options, but not sure how run and gun you're looking to be.