I would say it is about a grand to fix this up with a locker.

650 for an Eaton E-Locker ( I love mine) or an ARB (with an ARB you have to get some sort of air storage or compressor which is additional $$), 500 for a Detroit, (all full carrier lockers), 100-150 for a complete bearing kit). Re gearing is a great thing right now if you are going to do it, your choices are either 4.56 or 5.38 a gear set is about 120 or so. This way you can find a matching front differential. then another 200 or so dollars will go to install of R&P and the locker (yes a good shop will charge you the same to install both Ring and Pinion and locker at the same time) the grand total really shouldnt run over 1100.

It really isnt a horrible way to go although perhaps not the cheapest.

Cheapest is definently a junk yard axle.