I have a 95 P'up with the 4 cylinder fuel-injected engine. So far the truck has cost me
1) oxygen sensor
2) spark plugs/wires
3) fuel filters
4) oil changes
5) shocks
6) Timing belt
As you can see, the only things that I have replaced were scheduled maintenance items. I wouldn't give a shit if the truck crapped out tomorrow-- I have more than gotten my money's worth from it.
More mechnically expert people here could likely tell you for sure, but I think that the V6 in the izuzu line of vehicles was originally a chevy motor, and I think it had less of a rep for reliability than the 4-cyl.
For $400, you don' need very much time to recoup the investment.
You will not, however, be looking at any sort of awe-inspiring power.
ETA, I think you could expect 22-24 mpg on the highway with the 4 cyl, maybe lower if you run 17" rims. My truck ran 29mpg until I swapped out for bigger tires, and after 125K miles, it is only getting low 20s, which means that there is a problem that I haven't been able to diagnose somewhere.