Probably around 300 for that model, depending on the condition.
Honestly, I'd just keep it. You're going to get far better photos out of that camera than any DSLR out there (a 645 should be able to get you at least 30megapixel resolution scans). I'd be fucking PUMPED to stumble on that.
It's a great Medium format option, and not bad for learning to shoot MF. I'd learn to shoot a 35mm camera first, though... you can pick them up for cheap, and they're easier to find film for. Learning on Medium format would take some dedication, and some patience if you're a complete noob to film.
You're going to want to buy a light meter for the Mamiya, or buy a metered prism, but honestly, I'd just use a light meter. It's going to be cheaper, and more likely to work anyways.
Also, if you want cheap film to throw through it, you best options are here. It's what I use.
Have a nice day, Bluename.