Somewhere I got this Swift Tungsten Plate Armor and now I can't get rid of it just because its base value is 11550 so nobody I ever met in the game has enough to pay me.

I haven't discovered every area yet, I believe that the richest smith I met so far is the guy at Picaron Isle. His starting cash is 6000, but he still can't pay me for the armor.

I have no use of it (my character is a mage), but how could I just throw it out like a rotten apple?

Is there a reasonable way how to get rid of such item? (I would be willing to sell it under price but I guess that's not possible...)

Buy some stuff from the smith, sell him the armor, then sell the stuff you bought to another smith. That's about the only way to do it.

With my 2 mercantile, this probably won't be the best trade ever

Thanks though, at least I know I'm not missing anything

You can buy up things like arrows, which are 1 gold either direction with 2 Mercantile. Also, if you have Repair skill, buy stuff that is in poor condition and repair it before reselling to minimize the loss.