Some results from my research among the various futures brokers. I thought I'd publish them here if anyone's interested. The numbers here are commission (excl exchange fees) and an X-Trader subscription (except for IB and OpenECry, which has their own platform).
At 2,500 contracts per month ($ / contract):
Global Futures - 0.71
Interactive Brokers - 0.73
Variance Pro - 0.78
Velocity - 0.85
Advantage - 0.82
Open ECry - 1.05
At 5,000 contracts per month ($ / contract):
Advantage - 0.56
Global Futures - 0.58
Variance Pro - 0.58
Velocity - 0.69
Interactive Brokers - 0.69
Open ECry - 0.90
At 10,000 contracts per month ($ / contract):
Advantage - 0.28
Variance Pro - 0.46
Global Futures - 0.51
Velocity - 0.57
Interactive Brokers - 0.67
Open ECry - 0.82
Instituitional Accounts (flat rate but require $250,000 min)
Variance - 0.35
Global Futures - 0.24
The Instituitional accounts offer the cheapest commissions, but keep in mind that you're tying up $250,000 in cash that would otherwise be earning you some interest with a regular broker.