Depends on condition and age. A brand new Pelican 100X is $199 at Academy right now. FB Marketplace is all over the map. There are 2 100x's listed for $150 together, and others for $200-400 (with gear). Not saying anyone will get that, it's just what is listed.
If it's in good shape, and you are throwing in some gear to get someone started (paddle, leash, life jacket, etc)- I would say try for $150-200 and see if you can get it. if you just want it gone, take the first $100 you can get and call it a day.
Just my opinion.