I've converted my CJ5 to a Chevy 350. I'll make a long story short, $3000. I did all the work myself! That's $3000 in parts! I replaced an Iron Duke (GM 151 4 cylinder). I destroyed the T-5 transmission in less than a week! Now I have a Ford T-18.
If your on a limited budget, I'd suggest a remanufactured engine (or often called a remanufacture long block). The remanufactured engine will have a warranty. Seems some warranties are better than other, as well as some remanufactured engines are better than others. It would be possible for an average do-it-yourself weekend mechanic to get a remanufactured engine installed over a long weekend. I would venture to say that only a few experienced engine swappers could get a CJ up and going with a Chevy 350 in just a long weekend.
Another point I'd like to make is parts availabiltiy. It's easier to get the correct part (the first trip) for a vehicle when the vehicle is all original. Make minor changes to straters, alternators, belts, hoses, and if nessessary, emission parts, it's seldom accomplished on the first trip. This is not fun, when the only all night parts store is more than 20 miles from the end of your favorite trail!
I'll add vehicle value, if it comes time to sell your CJ, the more original CJ's tend to sell faster, and very often at a better price.
dave