For your budget, there are a variety of appropriately sized Vortech and Paxton centrifugal superchargers available on ebay. I would take a late 70's smogger 440, clean it up, fresh gaskets, summit k6401 cam with a new timing set. If you're crafty with fabrication, a bracket and pulleys could be setup with junkyard parts for cheap enough. 500hp would not be difficult to attain.