Easy decision financially lets just do the math...
Cost of additional maintenance assuming engine rebuild and possible transmission rebuild for the Monty: $6000
Cost of gas: you can calculate this depending on your annual mileage.

Cost of new car minus incentive: ?? probably >$6000
Cost of gas: again calculate depending on your annual mileage (this is where you may loose money versus the old Monty).

Which is cheaper over the short term say 3-5yrs? (probably Montero especially when you aren't making any payments and only need minimum coverage insurance)

Which is cheaper over the long term? (probably new car due to gas prices but keep in mind full coverage insurance cost while making payments) after +5 years depending on how far you have to drive.

If your wife really just wants a new car, buy a $500 used pickup, suv or 70's boat car to trade in! (or maybe there's some clause to prevent this?) <img src="/forums/images/graemlins/confused.gif" alt="" />