https://www.facebook.com/marketplace/item/740200543444097/ Might be up your alley if all you can afford is a budget Riv.
crusty & rusty 71 Buick 'boattail' Riviera for sale. 455 c.i. v8, 3 spd auto trans, 100,225 orig mi. Engine & trans are good but presently not in the car. Has some rust in the quarters and trunk floor but the rest of the body and frame are pretty decent. Also have some extra trim and a rear window. $2500 o.b.o.
rear windows are worth next to nothing because they never break 71-72-73 rear glass is the same, one of only a few non-mechanical parts that are interchangeable between the boattail rivieras when those rear windows are posted on this board they never sell and people end up throwing them in the trash:
Looks rough and if you start poking around it probably will only get worse. It sitting outside on dirt with the engine and trans out is a huge red flag for me. I would buy something like that to drive only if I went in knowing I would only fix it up enough to be driveable. Trying to restore it would be a losing proposition. Too bad cause I really do like those Riv's.