Check at forklift supply houses they often sell the better pallet jacks like Crown, BT lift, and Raymond. You can usually find a good working higher line jack taken in as a trade in for about 100 bucks. New 500 bucks to start. The higher line are better because you can keep them lubed, find parts, and adjust the forks when they start to drift.
Granger's Dayton, are also usually good units.
I have a crown that was at least 10 years old when I bought it I have owned it for seven, and it has lived in the back of the truck since I bought it.
What ever you buy make sure the fork alignment can be adjusted and there are grease fittings and the fluid can be topped off and changed.
Minimum lift capacity should be 5000 lbs.
Bob Wolf.