The guy that is selling the bench just reduced the price to $50
Only if you want to weld a strut under the pins. Then you'll be a day in a mask with a grinder taking the whole thing back to metal, priming and painting for a couple hours per day over the next 3-4 days for a cost of $100+ in materials (unless you're happy to leave it rusty). Plus the cost of whatever your time is worth.
You're buying a project. The difference between the purchase cost and free isn't worth haggling over. The question is whether you want this project enough to justify its costs. You'd get a brand new Chinese bench that will incline and decline for less than what the paint is going to cost. On the other hand, it's not made in China and maybe you really dig it - if for no other reason than it harkens to a time when a guy could knock up something in his garage for less than retail price - but you will have to earn it.
Flip it and have a good look at the underside. If you can bang a hammer through it, you don't want it.