getting another 88 trx 300 2×4 !!

Found a guy who’s son tore up the rear of an 88trx. Thinks the axel is broken. Says the rear end is not cracked or leaking oil. Wants $400 for it. Has powdercoated black rims, and metal framed mesh floorboards. The fenders have been wrapped in camo but a few spots cracking where fenders were run into trees.
If I need to replace a ring gear or a pinion how hard is it to shim the gears to achieve the correct meshing?