Time and cost all depends on how much of it you can do yourself. The '87 i am restoring came w/a bad rod. after pulling it down, the rods and pistons were fine, though I did need to have the crank turned. If the knock just started to happen(and the PO didn't run heavy oil to cover up the sound at sale), you may be lucky and not have any crank wear, though it should be checked anyways. I would think if you can do the work yourself you should be able to rebuilt it for under $1500. I wasn't on a time table to do mine, so I can't say how long it would take.
If you buy a complete engine, I think you could remove/install the engines one weekend, then complete the rest of the install the following weekend.