A selectable locker would probably not fall under the category of not spending a ton of money. If you are looking for something cheap then a drop in locker like an aussie or lockrite would be your best bet.
or... you could spend that money on a winch. T-rex is a great winch I've had one since 06 and winched lots and lots of big classic cars on my trailer before I put it on a reece hitch and mounted it on my bronco... I only paid $600 bucks for it and it's a 10k.
you'll still get stuck with a locker, it takes a lot to get stuck with a winch.
A bit more info on the intended use, as well as if its front or rear would be helpful. Cheap and selectable definitely dont belong in the same sentence together. For budget lockers, the aussie seems to have a pretty good rep.