The last major pre-owned purchase we made was a big steel squat rack. We got it for $60. It's huge, and super sturdy- we could get that much from it for scrap! The biggest thing was the guy couldn't really get anyone to move it! (And it was hellacious, even with our truck and three of us lifting... and my husband and I are both lifters, hence getting the rack!) We did have to replace the brackets, and since it's a non standard 3"x3" frame, they cost $70. So that added some cost, but anything approaching the quality would have been $800+ new.
A lot of our home gym is pre-owned, for that matter. We got our lifting platform free- it had been cut down by a gym that was replacing their platforms. We got it for free, and reframed it to hold it together. Works great. Proper wood flooring on the part you stand on and everything. Easily $200 in materials if we had wanted to make it ourselves.
Plus, all of our home gym spending has kept us from having gym memberships for going on... 3 years now I think? All in on our home olympic lifting gym setup I think we're around $800? In the same time, gym memberships at a *basic* place without oly gear would have been nearly $3k. For an oly gym? Try about $7,200. Crazy. And if we ever need to, we could sell our gym setup for at least as much as we put into it.