Buying a slide projector can be tricky. Many models have been discontinued (in particular, Kodak no longer makes its classic projectors), and this makes a good, inexpensive projector hard to find. However, there are a variety of online resources available for locating and purchasing a bargain slide projector; just keep in mind it's smart to look around to find the best deal.
If you don't know what kind of slide projector you want to buy, a good place to start is eBay's review site (see Resources). You should find a few different models that suit your needs, since you may not be able to find your ideal model.
Search for slide projectors on Craigslist.org and ebay.com. These sites are where you will find the best deals on slide projectors, although they often require some refurbishing. However, see Warnings for notes about Craigslist and eBay transactions.
Search for "slide projector" on amazon.com. Many Amazon vendors sell used or refurbished slide projectors, and Amazon is a bit more secure than Craigslist or eBay.
If you haven't found what you're looking for on either of the above sites, visit porterelectronics.com (see link below in Resources). This site carries a range of refurbished projectors, and they come with a 30-day warranty. While this site is generally more expensive than the vendors on Amazon, the products tend to be higher quality.
As a final option, go to slideprojector.kodak.com. This site lists the stores that carry Kodak slide projectors around the world. These stores sometimes carry refurbished projectors, although their prices tend to be higher than what you will find online.
Craigslist is designed as a service for locating products, not for purchasing them. Any transaction related to a Craigslist posting should take place in person, and you should never give any credit card or other personal information to a seller. eBay makes no guarantees about the truthfulness of a seller's product description. Check to see what rating the seller has before buying.