For the past two years, Reagan Elementary has an event called ROMP 'N STOMP. The kids raise pledges - per step or flat pledge for EVERY step they take during a designated 30 minute period.
All the kids get shirts to wear the day of the event. There are prizes, individual and class prizes like a pizza or movie/popcorn party. Local businesses donate free ice cream cone from Dairy Queen, etc. for some of the individual prizes. Big prizes are a bike, i-pod, etc. for most $$ raised.
There is NO investment except the advertisement and shirts for all the kids. You should be able to get some parent's business to DONATE the shirts w/ their advertising/sponsorship on the back. Depending on the size of the school, you may need more than one sponsor.
On the day of the event, the kids can walk, jog, run, play basketball, jump rope, etc. All kids have a pedometer and the numbers are recorded on index cards at the end of the 30 minutes. The child's name, grade, teachers' name and number of steps are on the card. Everyone has to sit at the end of the 30 min to be fair. It takes a little time, but great if you have lots of volunteers.
collect the cards and then give them another 10 days or 2 weeks to collect pledges. Kids GET EXERCISE AND raise $$ at the same time. NO SALES!!!