Inherited Rare Lens and Trying to Gauge it's Value

When my grandfather passed recently, I inherited his Vivitar Series 1 450/4.5 mirror lens. Apparently it's an awesome lens that they did not make for very long back in the 70's. It appears to be in great condition with all UV filters still stored in the top like my grandpa never touched them.

I am having so much trouble finding anything in regards to the value of this lens! While I hate to part with something of my Grandpa's, it will not work with my new Nikon.

Does anyone have any idea as to the value of this lens and how I should go about selling it?

Thank you!