I have been approached with the opportunity to bid for a contract making a 30 second spot for a small, Ma&Pa carpet cleaning business.  Being paid for this would be a first for me, and it's about time!  However, I have no clue as to what to charge.  I'm sure they will be looking for something simple and basic, for which I'm confident I can do a great job.  I think I could do a lot better then basic actually, and will even for less than the price of basic, just to get started.  I know there are a lot of variables involved in pricing such a project, so any pointers or clues or "ball-park" figures would be appreciated.  
Thanks,
Chris