I found that the best deal on microscope slides is from this ebay store. They do a buy it now feature, so it isn't like you have to bid and wait.
http://stores.ebay.com/Your-Science-...QQftidZ2QQtZkm
He used to have plastic ones, which are identical to the glass ones only shatter proof. However, they tend to cost twice as much. You'll want to think about which is more important to you.
He also had the best deal I've found for those. He doesn't seem to have them now, but you might email him and find out if he will get some in soon. I've never actually bought from him, but I have emailed him and he was very prompt and courteous. He does combine shipping so if you want to pick up some of his microscope slide mailers as well, it will be less in shipping.
Good Luck