If you want 550-650 from a small block, you'll want an aftermarket block otherwise it won't live long, so you're already out $1,500+, which is on the cheap end... for something like a Bowtie or Little M block you're at $2,100. You'll also be lookin' at aftermarket heads for that kind of power (unless you know someone who is REALLY good with factory heads, even then it's iffy), so expect 1,000+ for those. Rotating assembly (10-11:1 comp.), ~$1,500+. You're up to $4,000. You still haven't chosen a camshaft/lifter set, timing set, distributor, intake, carburetor, oil pump, tin (timing/valve covers, oil pan, etc.), water pump, gaskets, sealant, or (the most important part) machine work & balancing. The more power you make, the harder it is to make it on a budget with a traditional SBC... LS motors do it a lot easier, but it's still pricey. Your best bet is to shoot for 450-500 with an SBC and build it right, which is doable under 5k.