[EricH]

Start out by preparing a budget. Here are some things to include:

-Travel: How much it costs to go to your nearest event. (If it's a day trip, figure fuel, or the cost of a school bus, or whatever that is.)
-KOP/Registration: You know this from FIRST.
-Promotional items: T-shirts, buttons, advertising, anything that you're using to get your name out there.
-Materials: motors, metal, transmissions, you get the picture. This is anything that is not in the KOP.

If the total amount is over the school's limit, when combined with their sponsor limit, then you need to sit down with the school and bring this budget to their attention. Also bring the FRC extra materials limit--$3500--to their attention. (Note that this is for the robot only--but it gives them a hard target to increase to.)

You're not asking for unlimited funds, which may be what they're afraid of.

Other things that you should do:
1) Make sure that you're playing within their rules. If they aren't imposing this restriction on any other group, then you may want to ask them if it's a penalty for breaking rules without knowing about it.
2) Make sure that you know which groups the school already gets funding from--and then avoid them. You don't want to step on the school's toes.
3) Keep the maximum amount you can raise to a fixed amount. Right now, you have a total of about $6500 (registration and $1500) unless you go to multiple events, which I'd imagine the school isn't too keen on. See if you can get them to go up to $7500.

Your other option, which isn't really an option for this year: get the administration to your regional. Should do wonders for restrictions. (Actually, don't treat that as an option.)