I think the H3 came with a rear locker from the factory. At least most of them I think.
Adventure packages came with the locker, OP said base/lux, so no locker Aftermarket locker w/install would eat up a good portion of the budget. You can also do front lockers by swapping in newer front diff, but those are usually lower on the list of upgrades (mostly after you've grenaded your front dif )