When I'm trying to find out used vehicle worth I use KBB and NADA. KBB was already mentioned. Here's NADA:
https://www.nada.com/
As others have mentioned, used vehicles are in high demand right now, so their prices are higher than usual. You've chosen a good time to sell. I would do the internet searches and add on what you think is fair for the custom improvements and also for the low mileage. List it high to begin with.....you can always come down. Considering you are in the boonies, I'd list it on Craigslist first and see if you get any bites.
I'd also contact a dealer (or two or three) and email them your information with pics of the vehicles you are looking to sell and get their opinions. You will get opinions b/c they want to sell your stuff and make some cash. Tell them what your bottom line price is and tell them if they can sell it for you, they can keep whatever above and beyond they get for your vehicle. They can also do all the leg work to transfer it to where it needs to be to sell.