[WSSix]

You may find the LS3 crate engine from GM your best bet if you haven't bought anything yet. I'm referring to the 500 something horsepower model.

If you decide on a different path, the stock LS3 heads support a good deal of power. No need to go aftermarket typically. Not sure on costs but you may also find fully ported LS3 heads well within your budget. Or simply have your stock heads ported on the exhaust side to potentially save even more money and make good gains.