Write up a proposal and clearly explain why sponsoring your team is going to benefit him and how much commitment you and your teammates are willing to have towards the team. If you are only going to be out as a team of five guys on ten ocasions, then tell him that so that they know how much exposure they can generate.

The same proposal can be used for smaller local merchants. (more money is better than less)
Big Sponsorship - $1,000-10,000
Small Sponsorship - $300-500

The big guy gets all of the major space on the jersey (shoulders, side panels, collar, back), and the little guys get rear pockets and upper chest space.

check out champion systems, pactimo, and voler for good jerseys, but you can search the Road Biking forum for additional names as this topic has come up many times before.