Is there an order-of-magnitude estimate for the sell value of a paying royalty? I know one can go through the proper assessment (and sometimes it can cost) but we are looking for something to indicate whether this is a $2K - $10K value, a $10 - 50K value or something greater.

It is the 15th year of a paying lease in Butler Co, and has been paying in the $30 - $40/month on 7 wells of about 500 acres.  The payment is a share of the total Royalties. There are a number of owners of various %'s.  Thanks for any suggestions.