Re: how much to charge with only a kit lens?
Seriously, jokes aside, the kit you're bringing is no issue. f/2.8 is certainly no issue. Many event photogs shoot at f/4 on average - just to make sure the posing group shots look nice and sharp in the sweet spot.
However, since I'm primarily a flash-using photographer, I thinks its suicide to shoot evening events without an external flash & some diffusers/bouncers.
500D has decent noise control but since it is a cropped body, shooting at slower shutters would be a problem. With reasonably steady hands, I can shoot at 1/30 with a FF body (at a focal length of 24mm to 30mm) and get a sharp, well-exposed shot. You might struggle doing that with a 500D + 18-55 kit.
In light of the above, perhaps you might want to go FOC to build your portfolio? Just a suggestion...
Hope everything turns out ok!
Find me at http://www.dominiquekeephotography.com