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 3 G 8GB 8 GB Unlocked Extras  US $240.00
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 Apple iPhone 3G Black 16GB Perfect No Reserve Unlocked US $255.00
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 Apple iphone 4 Black 32GB Factory Unlocked US $960.01
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 8 Gb 3G Apple Iphone For Att Cell Phone Mp3 Cheap US $148.51
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 APPLE iPHONE 3G 16GB 3 g 16 gb Great Condition BLACK US $201.50
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 Apple iphone 3G White 16GB ATT or TMobile UNLOCKED US $212.50
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 Apple iphone 3GS Black 8GB ATT Brand New in a box US $400.00
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 Apple Iphone 3G 16GB Orange Jailbroken Unlocked 313 US $203.58
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 Apple Iphone 3GS 32GB Jailbroken Unlocked 313 Black US $385.00
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 Apple ATT Iphone 4 G Iphone4 NEW IN hand 32GB US $688.00
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 Apple iphone 3GS BLACK 16GB UNLOCKED BRAND NEW US $510.00
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 Apple iphone 3GS White Mint Condition US $315.00
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