94 Gmc Front Differential Question

I have been looking around for a new differential or possibly a good used one but i can't seem to find any other then getting one from a junk yard. I would like to rebuild that one that is on my truck but i was told it would cost me more then just buying one and putting it in. So my question is what would be cheaper? and also if anyone might have a good site of a company that makes differentials that woudl also be a big help. I just need to make sure i have 4x4 for the up comming winter since im only 6hrs from canada we get alot of snow.

By the way im gearing is 3.42 so hopfully that will help.