New and nearly new mags are $20-25 in the EE here.  That's probably going to be cheaper than paying for worn-out mags (some of which will certainly have to be junked due to wear/damage to the mag body, which is not fixable) and then paying for the supplies to refinish and refurbish the mags.

If you're finding USGI mag bodies for under $15 in quantity, it's almost certainly because those mag bodies are damaged or worn beyond the point where it's worth doing anything to them.

-Troy