Receiving offers to buy minerals


We have received a handful of offers to buy our minerals in 10N-11W ranging from 2000/ac to 4000/ac. We knew immediately that 2000 was too low since there is leasing going on at 1500/ac. I have been told as a general rule that mineral value is very subjective, but a good starting point is three or four times the rate of lease bonuses on a per acre basis in the area. That would mean even the best offer we have received would be considered low (3 x 1500 = 4500). We are looking for guidance as to what to counter any of these offers with, should we decide to sell. Any input is appreciated.