If you are in the United States, this is something you would want to look at – Refurbished iPhone 4 units; devices that have been returned or exchanged that have been quality-tested once again, are now available for cheap. You can now get hold of an iPhone 4 16 GB model at $99 while the $32 GB will be available for $199.
If these prices do not seem low enough, you can also look at one of these devices with “cosmetic blemish” – usually minor hardware issues that may not be easily noticeable. The 16GB and 32GB variants are available at a price of $79 and $179 respectively.
Do note that this price is inclusive of a regular AT&T contract that you will be bound for a period of two years. If the price sounds convincing enough, you can hit the AT&T site and make your online purchase right away.