It may be cheaper on eBay, I'm not sure, but if you want to get them right away try an office supply store. They make Business Card 'Peel and Stick' magnets that come in packs of 25. They are obviously business card sized, but you can make 6 to 8 pan-sized magnets per sheet.
I got great ones for really cheap at Michael's, a craft store. They are round, and I got about 30 for $3!! I would definitely check out a craft store before buying them on ebay and having to pay for shipping and all.