Generally, used prices will run half of new, or lower....then it depends on the market in your area and how many people might want what you're selling. Something as common as a sbc might be less then that. I'm not even a Chevy guy and have two of them around, one a 4 bolt roller cam long block, the other a 4 bolt mid 70's 350 complete carb to pan and I have less then $500 in both engines which IMO would represent the low end of pricing.