Recent Custer county leases I’ve seen seem to be landing around 3/16 royalty, with bonuses closer to $800–$1,000/acre depending on the section and whether there’s an option period. 1/8 options usually show a little more cash up front, but most owners seem to still try to hold the royalty when there’s a proposed horizontal well.
So your offer isn’t too low based on what I’ve seen
Since you’ve leased at 3/16 before, it would be reasonable to ask if there’s any flexibility on royalty or the option structure