Who is the least expensive online Commodity Broker with the lowest commission rate?

I currently use Farr Financial, paying $18 per option contract. Farr's "OK". Nothing special. I'm low maintenance, this isn't my first rodeo, when I ask the rare question I expect a prompt, accurate answer. Their reply is generally "HUH?" But I don't ask the simple questions, been there, done that. I generally enter a position in grains, or softs, by selling a put. Occionally I'll be igned the contract, so I'm looking for the least expensive online commodity broker for grains and softs options and contracts. I understand the numerous additional charges are all standard to the industry. Thank you for your time.