you can do quite a bit with $3000. If you have committed to this amount have the block bored, line honed and decked.
Get a nice internal balance crank and dish top pistons. Decent aluminum heads can be found on ebay for $800 or less, a 185-200 cc runner will be ideal, I'd like the 200cc's personally. Air gap intake and a cam with around 235-240* @ 050 and as close to 500" lift as you can get with that duration. 2500 stall and it will make serious power. Basically what Stroke said