Well, it's a lot easier to swap in a 4.0L, If you have a parts vehicle, you can do it in a weekend. A complete YJ is cheap. The only downside is that thwy will have a lot of miles on them but then you could do a 4.6-4.8L stroker. The only fabrication would be to move the horns on the frame. If you use a parts Jeep, you can sell everything off and recoup a bunch of it.
The only way a V8 would be cheaper is if you can fabricate and have the time to do so. Also, you'd be looking at a Carb'ed or TBI V8. Something like a 5.3L or better yet a 6.0L would cost way more then a running 4.0L YJ (whole Jeep). Then you're going to have to figure out what motor mounts to use, transmission, transfer case and axles. Radiator, wiring harness, gauges, adapters and all the small stuff gets expensive cast. You're looking at around $500 for an engine to transmission adapter and then another $500 for a transmission to transfer case adapter if you don't use a mated pair. I wouldn't even bother with a 350 though. You might as well go with a 383 stroker at that point so you're in the same neighborhood as an LS motor.
If you live in a state with emission testing you can run into more complications. Federal Law doesn't want to you install an engine that's not DOT. So you can get in trouble if the police really wants to get technical. ie., 4BT and Kubota diesels...
I've only seem Kubota's in Flatfenders. There was a guy who installed one in a TJ but it was slow. It's not as easy swap either.
While it's considered 'boring', a 4.0L is dependable and easy to work on. Not to mention, can just about be bolt-in. Everyone wants to be different and exotic though.
If you want to be different then do a SC or Turbo on your 2.5L. It's still a lot of work though.