I'm based in the UK so if you're US then I can't help you except to suggest the obvious clearers e.g. Refco etc. As a comparison, my clearer charges £0.25 per side for the first 5000 per month, then £0.20 up to 10,000, then £0.12 up to 20,000 and £0.08 above that. Obviously there's exchange fees on top of that which IIRC are £0.28 per side.