King Size Heated Mattress - what's it worth?

[Tsm1977]

I just bought a 2014 Flagstaff Pop-up Camper. When we picked it up, we noticed a very small tear in the king sized heated mattress. Instead of swapping it out, they sent me a new replacement mattress. Now I have a brand new king size mattress in my garage taking up a lot of space. I would consider selling it, but I have no idea what it is worth. Does anyone know where I can find out? A quick Google search gave me few usable results.