They Run about $50-$100 here for a pull out gear and differential, $150ish for the whole axle Assembly, idk if you have friends or family in the states but would be cheaper to source the parts that way. There also plentiful at most junkyards since no one really bothers with the 7.5 ford rear end and you can find both those gear ratios and a 7.5" Trac lok from production cars / trucks.They where some rangers and Explorer, but I don't think as much to find parts that easy. Plus here they will sell a used rear end for about $400-$500.
Also know I will never do an engine swap since its almost Impossible to find a V8 from a mustang Gt. There are a lot of 302 in junkyards but with a carburetor lol.