For land values then and now: Call the tax office in Lea county, NM - call the county appraiser - call a local title company and ask for referrals to realtors who sell in your area. I would guess that any/all of these people may be able to help you. Don't forget to check court records. County clerks can be helpful
The company who is making you the offer is not going to "smarten you." Be aware that not all real estate is passed on via probate. Depending on what state, sometimes it's deeded via Muniment of Title.
Good luck
Pat