Gazza the first aim should be to do something quite big in the town centre. outside debenhams or something get people to express a interest let them see what its about.
If you do not read the adver then no one will know about the cost unfortunatly
If you wanted to do something of that type, you need a license from SBC...they'll have a strict timetable of any groups who are allowed to do stuff in the streets....if you don't have a license you'll be hooked by OB.