The eBay website is an well known auction website, with quite a good reputation among those who want to sell stuff. However, among those interested to buy items off of eBay, this website will most likely not be their first choice, unless the item is rare. This is due to the many counterfeit products being sold on this site. However, if you want to give it as try when searching for a cheaper Samsung Galaxy S, below you'll have some choices.
You can get a brand new Samsung Galaxy S 4G, which you normally get from T-Mobile in the United States, for $365, from this page (expired now) or from here for $380. The sellers of this item received 100% positive feed back so far which is a good sign if you want to buy from them. But be aware of the fact that you can get the item for less, from other places.
If you visit this page, you will be able to see all of the models of the Samsung Galaxy S available for buying on eBay, and this link will always have an updated list of these mobile phones, so you won't risk landing on an expired auction, like above.
The number and selection of models of Samsung Galaxy S cell phones are quite extensive. You can find the cell phones sold by Verizon, T-Mobile, AT&T, Sprint. The phones can be brand new – and in a sealed box- like the ones presented earlier, unlocked, used, or even refurbished. It's only a matter of you seeing the item you're interested in, at the right time, in order to get the best price. Most of them, if not all will have at least one image so that the buyer won't have to go elsewhere to see the item.