If you do get the $500 within the next week, I've got a suggestion.
Don't let the team members that didn't do any work on fundraising know that you made the deadline--yet.
Then, at the next team meeting, you, or better yet, a trusted mentor who's in on the game announces that because A Certain Group of Students couldn't be bothered to fundraise, your team is short X amount, and therefore can't register. Because you can't register, you can't compete, and if the Certain Group of Students had raised $Y apiece, it would have been rather easy to pay registration, etc, etc.
After the news sinks in and they start complaining and wondering why (and the point gets hammered home by repetition--you didn't raise enough, so you can't compete), you announce that A Different Group of Students managed to raise $500 at the last minute, and the status given was a week old. Because of that, you can in fact compete, but you will all need to work hard like the Different Group of Students. Oh, and by the way, that includes raising funds to help with building and travel (whether you actually need said funds or not, it's always good to have a little extra).
If they don't start complaining and wondering why, then it's probably time to shrink the team. Give me 10 hard workers who are willing to learn any day over 50 people who don't do any work, even if those 50 are more qualified. (Also applies if Certain Group of Students keeps being not-productively-busy without good reason.)
OK, now for some suggestions for places to get money:
-Chamber of Commerce
-Parents/grandparents/other assorted relatives
-Small businesses
-If a local mall or somewhere like that has a fountain, ask if you can collect the change that gets thrown in.
-More demos.
-See if another local team can give you a loan/pay part of your fee outright.
-See if FIRST can arrange to give you more time. (Of course, announcement of more time should you get it could easily be handled like getting more money above.
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