I had one of the dump bed inserts a few years, ago. Found it in an old IH pickup at a local junkyard and paid $350 for it. It worked pretty good unless you overloaded it. I used it for about five years and then sold it for twice what I paid.

Here's a link to a dump bed conversion that might interest you. It gives you ideas on building your own setup, at least. I have seen guys do this conversion from scratch using old hydraulic parts and some scrap steel.

Pierce Arrow Pickup Truck Dump Hoist Kit — 4000-Lb. Capacity, Ford 1973-98, Chevy/GMC 1973-87 and Dodge 1973-77 | Lift Gates Dump Kits| Northern Tool + Equipment