cost of engine blocks

No way would I pay 500 for a bare block. That's what you're asking, right? Basic long block, yes. Bare block maybe 100 bucks. And since the 340 is almost a unicorn now, you cannot lump them in with the rest. They usually start out around 300 and go up for a bare block.
^^^^
Agree , I paid $500 for an untouched 440 w/ the trans still bolted to it , pulled as one piece.
You don't have trans to engine alignment problems that way either .