I was going to say go w/the auto for mud... and get the biggest cooler you can afford.
Here's the cheapest way I can think to swap out w/your budget: grab a running Chevy 350, w/the 465 and married 205 out of any pre-'80 3/4 truck (or a 2wd model, either or... but the 4wd have the 205, and it's just better than stock). Then email Spicergear for pics of his super simple motor mount adapters, they'll cost you literally about $10. Then spend a six pack for your welder buddy (we all have one!) and have him make you a tranny mount. Spend a little more getting the driveshafts sorted out. With all the cash you have left over, buy a gasket set for the 350 and install it. Maybe a cam if you feel spunky.
I don't think there is any way that's cheaper, and at the end of it you'll still have cash, AND a running truck.