My main source of transportation are motorcycles, so I mostly use my PF for 4x4 travel or when I have a broken leg (true story). I have a two-year plan to save for a Cummins crate motor to install as part of a full restoration on my 95.
I know this doesn't answer the question of an economical swap, which I have seen many that are very good for very little money, but more to the point that an engine swap is a spectrum and there are many places to land. Cheers and good luck.