I grabbed an engine off the clearance sale. W2 classics, magnum style crate shortblock, delivered for $2175. There are some really good bits there. As for what you want, you dont need anythign that exotic to make reliable 500hp on pump fuel. A more realistic budget figure with a flat tappet would be closer to $7K soup to nuts, and with a solid roller closer to $8500. With a dyno test and break in, I can't see it going over $10K.