Look on your city’s Craigslist page. You can find a decent used engine for just a few hundred, or a completely built motor for couple thousand. In Oklahoma City, I can usually find a Chevy 350 and matching transmission for less than $1,000 dollars.

It all depends on how well the engine/tranny run and how much of the original performance it retains over its lifetime, the length of which is also a factor of price. I wouldn’t know actual prices, however, but a few engine replacements I’ve seen can top $5,000, more if it’s a significant engine.

It depends on what you want to build. I’ve seen crate engines going for less than $500, and you could go even cheaper if you were willing to check out a few junk yards. You do have some things going for you: a truck of that vintage has a cavernous engine bay, so you would have no difficulty dropping a new mill in there. You probably have the 216 CI six. The motor mounts would be compatible with the small-block V8 that was produced in great abundance from the mid-50s up to the early 2000s. I would suggest getting something built in the pre-EPA era to save yourself a lot of grief.

When I was in college, my roommates and I pulled a 235 I6 out of a ‘59 Chevy and dropped in a 283 V8 and tranny in around 5 hours, with just a tackle block and hand tools. We bought the engine and transmission from some pig farmer outside of Wooster, OH for around $100, but this was in 1968. Considering the millions of small-blocks that were made, you should be able to find something suitable without paying a ton of money. I would check around your area for Chevy hot rod clubs. They could probably hook you up with the parts and the labor to do the job. A ‘48 pickup would make a bitchin’ rod if you outfit it with side pipes and new paint.