Brad, it's been so long since I've worked on the twin I-beam set-ups I can't really remember - but the kids truck needs the front end gone through before winter.
The really bad part about these is once a tech gets into them, there are so many things to consider and they can all drive the costs up. Questions you'll need to ask yourself... do you do only the affected side and wait for the other side to go? Do you do both sides? Repack the front wheel bearings while in there? How about the brakes - are they getting close? Would the rotors need machining or replacing? The spindle bearings can take quite a beating... should we replace them or hope that cleaning and repacking will be good? The center joint (on the right side of the diff.) likes to sieze and is impossible to diagnose until you get there....it's possible to change this joint without removing the diff. but it takes a certain amount of finesse to do it in car without breaking stuff. Has mother nature been kind to the front end or is it going to be a rusty nightmare? Are the ball joints loose?
Given that the truck is 25 years old and I'm not sure if it's your pride and joy or if it's a huntin' truck beater, may colour your decision.... I can only suggest taking it to a shop that is familiar with 4X4s and getting a written estimate.... you might even want it priced out both ways....simple fix and worst case scenario...
Cost-wise, labour rates vary across Canada way too much to accurately give dollar signs....I'd expect 2 or 3 hours to do one joint... 6 hours or so for the full meal deal.
Sorry I can't be any more help than that....