Although not completely original, going to school/college/uni/work etc in fancy dress would grab attention and make people laugh, they'd probably put money in a bucket then. I did a sponsored slim, which everyone who called me fat took the piss out of, but that was okay because it got the attention I needed, and managed to raise £450 for charity!
run an event! like a party, race night or whatever i've had to raise £2500 over the last six months along with a few other people, and we've done all sorts! party works super well though, you can get around £400-£500 but events work super well!
either that or a sponsored event, i cycled coast to coast and raised around £300 and i know some other people did a twelve hour hike and managed to raise around £200 each
The event you mentioned, what kind of stalls would you have on it?
Do you think it would be worth getting a bouncy castle?
Do you know how much school halls cost to hire?
often, if you tell people what it's for they'll give you it for free or massively discounted depends what sort of event, you could have like a coffee morning or a craft fair or just a general fair and get people to pay to have a stall and a percentage of the profit they make or something