A completely (properly) rebuilt engine could easily cost you a couple thousand bucks. And unless you can personally verify what was done, purchasing a "just rebuilt engine" from some total stranger might get you something that's not any better than what you've already got.

You say you don't have the equipment for a complete rebuild, but I'm wondering if you might be able to pull off something a bit less extensive that would still result in a reasonably refreshed engine. Unless you have tons of miles on the engine, and assuming the bottom end is still sound, possibly you could get away with something like:

Pulling the head and having it rebuilt at a machine shop.
Ridge reaming the tops of the cylinders.
Pushing the pistons out, likely honing the cylinders and popping new rings in.
Installing a new oil pump, cam, and lifters.
Possibly having the distributor rebuilt.
Putting the thing back together with the original bearings in their original positions. (Or new bearing inserts??)

Special tools like the ridge reamer and damper puller, etc. can often be checked out from an auto parts store with a security deposit. I'm thinking you could get in and out of the project for around $500-$700, but I live in the dark ages.

I'm not an engine rebuilder, so I don't know if this idea is crazy or not. But others on this BB are well versed and will hopefully chime in. After over 30 years of driving Volvos (granted, not the same one) I've never had to rebuild one.

Good luck, what ever route you take.