you and the buyer to get separate appraisals on the land, compare notes and meet in the middle. An appraisal should be around $300, maybe less since you don’t have anything built on the land. But then at least it would be two expert opinions.
If you feel ballsy, maybe ask the buyer to go in halves with you on one appraisal? Just be sure you both research companies and hire a reputable appraiser in the area.