Help! Mineral lease $10 per acre Bakken near Plentywood Montana

My aunti and her family have minerals around Plentywood Montana. I am sure it is in the bakken. (640 acres) They have not had it leased for several years. She recently got a lease offer for $10 per acre and 1/6. I told her we just leased or family acres in ND for $500acre and 18.75% royalitys. I would like to advise her. Can anyone tell me what minerals are going for around Plentywood Montana? Also could you recomend a leasing company active in that area.