Mineral RIghts in Eddie County

My mom inherited Mineral RIghts in Eddie county from her Mother years ago. We just rcvd an offer froma Denver compnay. I want to get a sense of the value before signing. SUggestion on who to reach out to. Below is the legal description: 20 acres S2SWSE Sec 18 18S 26E, Eddy County, NM, 20 Acres E2NWNE Sec 19 18S 26E, Eddy County, NM, 80 acres N2W4 Sec 11 20S 25E, Eddy County, NM.

Suggestions where to check valuation. Over is less then $20K