If you have a 7.5" rear end (came in 4 cyl and 3.0 v6 Rangers) don't bother doing anything to it, it would be a waste of time.
The best low cost solution is to buy a complete rear end out of a '95 to '01 Explorer. It is a 8.8 with 31 spline axles and disk brakes, the wheel bolt pattern and width are the same as the Ranger. These can be purchased for $200. to $300. complete.
The 4.0 6 cyl Ranger axle is a 8.8 but only has 28 spline axles and drum brakes, they hold up OK but the swap would still be worth it IMHO.
Good point! Yea they run any where between $200 up to $500 depending on the gear ratio and the core exchange. You can even get a stock one with a 4:10 gear ratio! I can help some one track one down if any one is interested