Hi David... as you may expect, there will be a lot of variables to this... so, I'll just tell you my experience with this.

I found a fresh, low miles 73 455 with 6X heads, just needed final assebly (short block) for $700.

You can often find a nice running Pontiac "Big Car" with a nice 400 in it for maybe $500 for the whole car, and still sell some parts on ebay to make some money back to pay for a tranny!

I would think you should be able to find an engine and tranny for $1,000-$1,500 that would get you going and keep you going for some time to come!

Good luck, hope it works out! - Brett