My personal approach will be to buy old & cheap and set aside cash to either dispose of it or rebuild it.
The lower the purchase price, the shorter the service life you need for it to pay for itself.
Buy cheap enough and you can scrap it in just a couple years without crying, or afford to have everything done over if you like it enough.
Chances are, I'll probably just buy one cheap sleeperless power unit after another since the whole truck costs less than a motor rebuild.