Need estimate for worth of mineral rights

Could use some help in estimating the fair market value of mineral rights...have a relative who has expressed interest in purchasing my sister and my rights and they wish to pay the 'going rate' that we could get elsewhere. My sister and I both own 3.333 acres for a total of 6.666 in the following area:

Many thanks for any help from the 'experts'!

mineral ownership for vertical wells are in Section 8, Block N, HE&WT RR Co. Survey, A-633, Upton County, Texas. Property name: Pembrooke Unit Tract 4 (0.00130200 RI)

1/2 ownership in my name; 1/2 in sister's name...acreage 3.333 each for a combined total of 6.666 Old vertical well RI 50% each 0.00065100;

3 new lateral wells allocated to our property:

1. Property Brook M 1B #2H # 932605-002 SHL: 2453' FEL & 2453 FNL Section 9, Blk N, HE&WT RR Co. BHL 2338' FEL & 2550 FSL Section 1 BLK M, EL Each 0.00034909 RI;

2. Property Brook M 1C #3H # 932602-001 SHL 2408 FEL & 2453 FNL, section 9, Blk N, each 0.00035081 RI each;
3. Property Brook M 1A #1H # 932604-001 SHL 2498 FEL & 2454 FNL, Section 0, Blk N. 0.00034903 RI each