The only problem I see with buying our own prizes is having the left overs after it's all finished. We use a carnival group called Fun Services. They come in - bring all the games and inflatables- the kids get tokens, we cash it out and it's gone from us.

If you are going to go with larger prizes - here is a thought - you know all those crane games around town with the little stuffed aninmals and such in them. Well someone has to own the cranes and have the inventory to put into the machines. In our community it turns out to be one of our school families. Just a thought.

Great ideas FisherQueen. I would have never thought of asking stores for day old baked goods -- these are still great tasting, even when they are outdated.
I'm going to try this for our Spring Fair-- when we do our cake walk.

If you are planning a cake walk booth then I would check with your local grocery stores. They are usually happy to donate their "day old" baked goods for a worthy cause. I've been picking up "day old" goods every school day since October from one of ours for the school to use as after-school snacks for the LEAP test tutoring program. Normally I get donuts and cookies but that is because we requested finger foods. If you tell the store manager what you are doing then he can give you cakes. We've gotten some cakes on various days and the teachers say they are so fresh that you cannot tell that they are "day old"

Also, if your carnival is after a holiday, like Valentines Day or Easter, then you can pick up bagged candy very cheap at WalMart, etc. These smaller sized candy bars can usually be handed out as prizes for some of the booths as well.

We have catalogs with tons of prizes. My favorite is rinovelety.com, also goodtimeattractions.com, or ustoys.com

Sav-On-Closeouts.com | Wholesale Novelties, Crafts, and Seasonal Products. Your closeouts source numerous items cheaper than OT

We always used Oriental Trading, but I know there are other similar companies out there. They have lots of little items that you can buy in bulk for pretty low prices. One good thing about the non-perishable prizes is that you can save them for the next year. That was why we used those types of things for the most part.

As for how much to buy:

Have you had other events? What was your attendance at those events? Otherwise you could just make sure that you have a prize per student per booth and then add some extra for younger siblings.