How do you define "decent trading volume"? Over 10k/month in commissions? I think commissions are negociable if you have large enough trading volume.
You can't negotiate with them, as i already tried. THey refer you to the unbundled structure whichs is fine except for the exchange fees Same think happen at TS. Exchanges fees kills you. Even if you're making above 20 or 30k contracts per month on globex.
so you need to investigate the different options for seat lease or purchase if your clipping enough size/spins to make the exchange fee's significantly more competitive