We all like to go a good deal, and when it comes to finding an iPhone to a reasonable price, the best place make a good deal is not at the phone house.
When I want to find a product to a cheaper price, I always do a search on the Internet, and quite often I end up at eBay. It's really hard to beat when it comes to making a good deal.
What I really like about eBay is that you can find both unlocked and jailbroken iPhones, but new and slightly used ones. If you are not that technically minded (I'm not), it's great to get the iPhone ready to use.
You might not want an unlocked one. I do. I prefer to choose my mobile supplier myself. And as for the jailbroken thing it gives me the freedom to use other apps than what I can get at Apples App Store. Nice 
See if there's not a good iPhone deal for you too:
 Apple iPhone 3G 8 GB Black ATT NO RESERVE  US $290.50
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 Apple iPhone 8 GB first generation ATT GSM US $172.50
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 Apple iPhone 8 GB ATT Cell Phone US $122.50
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 Apple iPhone 3GS 16 GB White ATT US $420.00
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 Apple iPhone 3G 8 GB Black Unlockable US $320.00
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 Apple iPhone 3G 8 GB Black ATT Brand New US $411.00
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 Apple iPhone 3G 8 GB Black ATT US $202.50
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 Apple iPhone 3G 8 GB Black ATT Used Apple Care US $195.50
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 Apple iPhone 3G 8 GB Black Unlocked US $330.00
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 Apple iPhone 3G 8 GB Black UNLOCKED ATT T Mobile US $215.50
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 BRAND NEW ATT APPLE IPHONE 3GS 32GB 313 FW US $580.00
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 Apple iPhone 3G 16 GB Black ATT MINT unlocked 3gs 2g US $310.00
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