Your used engine is going for 2000-3400 dollars plus shipping and installation. I worked in salvage yards for many years and just want to warn you that they can pull many tricks in mileage and condition of parts. You will have to do your homework. If yu need suggestions let me know.
Since money is an issue, you may want to find if other type Isuzu trucks that year may have engines that will interchange and go for that.
Noone will know the difference except you