How can i fix my broken seat belt for cheap?

I have an '89 GMC S-15 pickup and the penger side seat belt is broken. The shoulder strap is completely loose it does not recoil back into the spool when you take it off... the strap around the waist works fine just the shoulder strap is broken. I want to fix this the cheapest way possible but I need a good solution. Any ideas? or how i could fix it myself?