M.K.
Try Zurchers. I have gotten some very reasonably priced prizes there. There is one off of 2100 south or by Babies R Us in Midvale. I would try that first.
I would also check the dollar stores. And another place is Target. Right in the front they have a whole section of stuff for a dollar. When you are buying a lot I know that can add up but sometimes they have some fun stuff and maybe you could get a couple of "grand prizes."
I have also found some fun stuff for kids at Tuesday Mornings. This is more in the way of games, like travel games or blocks or something, but maybe worth checking out. A little more money though. But you never can tell what you might find there:)
Try ksl.com just for fun.
If you want to get candy bars, or candy, as a prize the cheapest place that I have found is costco.
Other places that often times has a little dollar section are craft stores and you can get some fun stuff for kids, and adults. Try Johanne's or Michaels for the best prices.
Good Luck!