Typically these outfits that want to buy your minerals will send a draft and an offer to purchase your producing minerals. I receive these offers occasionally and they go directly to the waste basket. I would not know how you would get an appraisal on your mineral property, assuming if there is no production. Your statement sounds like you have no production currently. How would you evaluate what may or may not have any value? The Appraisal Districts in Texas assess mineral properties for ad valorem taxes only if they are producing.
Harrison County has been active with drilling activity in the Cotton Valley and Haynesville Shale recently, according to the TRRC W-1 reports. If you can disclose what Survey your mineral property is located it would be easy to tell what activity is around your immediate location. I would be inclined to hold on to the mineral rights.