I'm running into the same problem - cost of a crate vs. cost of work required to rebuild a used block with new parts.

In my case I'm planning a 383 build early next year and I'm finding it hard to beat the cost of an off the shelf ready to run short or long block. Even a GM Performance Parts HT383 short block with pan, balancer, and flex plate at 3200.00 is hard to beat from scratch. GMPP 350's are MUCH less expensive than that.

What I don't know is how well balanced a GMPP crate engine is.

Other suppliers of crate motors can be even less depending on what you want inside.

http://www.speedomotive.com/ht_383_tow.htm for example offers an HT 383 starting at 2395.00 for a new GM 4bolt short block with high nod crank and forged pistons and rods, all balanced, blueprinted, and ready to use. I can't beat that from scratch around my area.

Shop around as there seems to be a lot of value available from crate builders.