Wow, lots of negativity about the V8 swaps. Who here actually has experience with V8 swap costs, particularly when it comes ot SBC's or SBF's? I'm not saying anyone is wrong, I just want to kinda put people into perspective here. If you don't know for sure, then you don't know do you?
A SBC can be swapped into almost anything for under 1k if you're doing your own fab work on the mounts. Even the 5.0 swap into a miata is extremely affordable, and that's a more expensive motor to work with from the get go. One of the big things that makes these swaps cheap is that most parts you'll need can be bought out of a catalog for cheaper than you could probably make it yourself, like exhaust manifolds.
With aluminum heads and intake you can get them in running shape well under 500 pounds, and the bulk of that weight is much lower than most other engine options. And with those little go fast bits you'll probably be over 300hp with ease. Going carb'ed makes them extremely simple on the wiring end. Only need like 3 wires to make the thing run and charge the battery (12V to dizzy, electronic choke wire, alternator BAT cable). This makes them weight/wise comparable to a heavy 4 cylinder, with as good of handling potential as almost any 4 cylinder. The extra 75 pounds or so it adds over the lighter 4 cylinders is closer to the ground and easily able to be compensated for when it comes to chassis tuning at the track.
As long as they FIT into the bay, it's a cheap swap. And I KNOW the S12 can't be THAT tight. So here's a rough cost list (off the top of my head, so forgive me when I forget something)
Motor ~ $0-200
Trans ~ $50-150
Mounts ~ $30 in plate steel
Exhaust Manifolds ~ $250
Exhaust (from shop most likely) ~ $150
Driveshaft ~ $100
Odds and ends (throttle adaption, bolts, etc) $15-100
That's a max total of a whopping $980 if you're budget shopping and being smart. This also requires you either know someone with a welder or own a welder. Most of us have a friend with a welder that would do the work for the price of some beer.
I know i'm from the Z arena, where we have larger engine bays which are easier to do swaps in, but even in the older z cars a SBC swap can be done for literally almost nothing. I've seen it done for under $300 total. That's the appeal. Dirt cheap power with plenty of potential for a light car.
Now, to play my own devils advocate, these swaps aren't for everyone. A V8, especially a carb'ed one, has a very particular nature/character. They're monstrous to drive on a daily basis with a lot of fine tuning, and they're generally loud and obnoxious. But they're a lot of fun in their own way. You can do many other engine swaps for not a whole lot more money and have a completely different car in the end. So any person considering an engine swap needs to really consider what they're about to do. Don't just choose something because it's there and available, unless you're that type of personality and don't mind doing all that work that might just be done over again with a new motor in a few years.
And as to the VH and 1UZ motors, they're awesome. But the manual trans conversion alone is crazy expensive. I'd have a 1UZ in my Z if I could put a manual trans on it for under $500, but it simply can't be done. If you have that 5k budget for a build, sure, consider them. But I wouldn't do a 2k build and spend a third or more just get a trans on it.