Selling mineral rights

What are mineral rights selling for right now? Our family has 900 acres currently leased until 2017 and the discussion has tuned to one of the family members wanting to sell. Others in family may want to offer to buy the one members rather than lose them in the future.

I am absolutely no expert, but right now, with oil being below $50 a barrel.....I'd say they aren't worth much. Just a guess.