Valuation for oil royalty interest held in an IRA

Before I decide whether or not to acquire a producing royalty interest through my self directed IRA account, I need to be able to value it per IRS and custodian bank requirements. Is there a cost effective way I can get such a third-party valuation from a credentialed individual (CPA or other valuation expert)? I am thinking a PV calculation based on the run statements, which I can do, but it has to be third-party and done annually. Referrals welcome. Thanks.