Do this. Take a team photo in a nice location with any robots if you have any. Photoshop it to have text at the bottom that says "We proudly support XXXX Robotics Team" Get them printed then make/buy some sort of nice frame or something to put it in. Next, make a binder containing approximately 6 pages with pictures and information on FIRST and your team. Make one "plaque" and one binder for each team member to solicit. Go around to local businesses (seriously, just walk in asnd ask for the manager/owner, it works) and show them your binder and tell them that for a small donation of $100 they can have this really nice plaque to hang on their wall that shows their customers how suportive they are of the community. You may even let them keep the binder for a couple days to look at it, and then you can go back and pick it up, hopefully along with a check. Additionally, tell them you will recognize them as an "official sponsor" and put their name on your team shirt and robot and website. See, then you will have # of team members x $100 worth of money.
You should practice your speaking skills and what you will say.
Keep in mind that if they say no, tell them any donation they can make would still be greatly appreciated (but don't say this until they turn down the $100 deal).
Here is our binder that we used (sorry its tripod)
http://cmr696.tripod.com/ and here is our plaque
http://team696.org/plaque.jpg to give you some ideas.
In each of the past two years, I believe we have made $3000 - $4000 dollars by doing this.