It all depends what the charity you donate it to sells it for.
My wife and I donated our second car that we realized we hadn't driven in nearly a year recently and our local food bank was able to auction it for just under $5,000. We got a tax form that listed the car and what they sold it for a couple weeks after that.
I'm not sure if there's a limit because if someone is willing to pay $100,000 for a sweet RV some rich person donated at auction then, as far as I'm aware, that rich person would be able to claim the $100,000 as a charitable donation.
Please correct me if I'm wrong though, because this is just an educated guess!