Price of rock varies all over the country. Here it's expensive because it all has to be brought in. Native stone in an areas it's from is always gonna be relatively cheap. You'll just have to price it out, then take into consideration the labor and time it will take to disasemble and remove your stone. I'd guess half or a third of what it will cost sitting on a pallet would be about right.
I'd give it away just to get rid of it, but it sounds like you like them sitting there. If it's something you enjoy and will miss, then a couple hundred bucks is hardly worth it.
If you decide to sell them, be sure to get payment first, and also be sure to include a clean up deposit. Decide how long it will take you to clean up his mess and what your time is worth to do it yourself, then add a little to that number. I've gone as high as $1,000 before, but $500 is usually enough. Tell them there is a time limit, or it must be cleaned up to your satisfaction. If not, you keep the money.
I've found this does two things. It will change there mind and they won't even want it anymore, or they will do a really nice job of cleaning up after themselves and not destroy your land. It's a win-win for you. More cash if they trash your place, or you get a quality job and no headaches.
Good luck,
Eddie