I bought a "short" block off a guy in Illinois for $75. He was parting out a '66 Mustang Convert to install a 351W or something. The guy stated that the rebuild was done by the person he bought it off of and it was a "standard" rebuild. I checked everything and found that the #1 con rod didn't match the other 5. It was 17 grams too light and 0.030 too short. So the moral of the story: yes, you can save yourself a ton of cash by buying off of another person versus the machine shop; but check EVERYTHING. If you go thisroute buy yourself a dial indicator and a set of calipers, minimum.
A "short" block is the block, along with the crank, pistons, rings, cam, etc. A "long" block is the short block plus the cylinder heads that include the valves, springs, retainers, etc.