Buying a used gt40p head off the internet or a junkyard and you WILL be: replacing valve springs, seals and givng them a clean up mill and cc. Or cc them and mill them more to get the compression up. Thats a good $350 right there into your used "budget" head. So figure you get them for around $400 + the min of $300 you'll be pulling into them. Might as well up your budget for a good alum head assuming you wanna do it right.
The camshaft is the key to making power. The b/e cam will not be what you want.
I think my friend is still selling a set of older model edelbrock performer 5.0 alum heads. I think he wanted $600. Let me know and i'll ask him, he posts on here too.