Check out the net, for example
http://www.runningusa.org/events/RMindex.html
I have put on a local 5k for 13 years now, and can tell you that it is a big chore. The participants enjoy themselves, but there are a thousand and one details that you'll want to get right. I bought a book about organizing road races, and talked to local race directors. You can get some freebies from Running Times and Runners World. I get college students to go around town and solicit gift certificates from businesses, to use as random draw prizes. We got more participants after we became associated with a local charity, ie: the proceeds will be donated to XYZ Charity.
I look at putting on a race as a way of giving something back to the local running community. We give out high quality cotton t shirts, and nice prizes. I think that people appreciate that, and they like to come back. They know it if you give out cheap crap.
Basically, races are a break even prospect, at best. The costs come close to the revenue, if you plan it right. The only reason there is any money left over, is if you get cash sponsorship. That's where the charity thing comes in handy.
Best of luck. Let us know how it goes.