If OP can get 21k for this game good for them. Yay capitalism. If you bought a house at the bottom in 2011 would you not accept its current re-inflated value now?
I'm certain the actual cost of TBL came in much higher than ARA or DP thought. Remember making 3 prototypes vs a run of anything is a a difference as wide as the universe. DP probably tried to hold ARA to an unsustainable earlier quote (because DP couldn't afford the increase) and ARA said "screw it".
Also there's no way the license hasn't expired by now.