You can do a 5.2/5.9 Magnum swap for pretty cheap, especially if you already have a 4.0/ax-15 combo, since you can easily use the ax15 trans. tons of info on this, the wiring is extremely easy, plus you can always view my build thread and ask questions on there if you had any. Good luck with your decision!
I may add though, I know quite a bit about the various TDI engines as well, and if i had a much larger budget, that wouldve been my go to swap.