Well matey, that will depend on yer average monthly volume with most brokers. This means you will have to do some "negotiations" and I don't mean the cannon ball and musket type of negotiatons. That be easier. Aaarrrrrrrrrgh...
The cheapest futures broker depends on a number of variables. Quoted commission rate is only part of the true cost. Other possible costs are platform fees, data fees, software fees and interest rate paid on margin cash. The best rates available are for exchange members who do big volume, have a large account balance and deal directly with a clearing firm. Retail traders rarely can get the same rates. The lowest published retail rates I have ever seen are from Eagle Market Makers. ES starts at $0.40 a side plus fees for a total of $1.55 a side. But you have to pay for the trading platform. Only makes sense for volume traders.