Here are your options for fixing a screen:
1. iPhone screen will repair by Apple costs $199.
2. A myriad of 3rd party vendors who will replace it for $100-$150.
3. A do-it-yourself replacement kit from iFixit costs $65
4. A do-it-yourself kit on Amazon costs $11.95.
Why this much difference then in the prices for the same problem?
I think most of us then repaired by yourself to save a cost of $65 - $11.95. Amazon is amazing for that.
Another tip : the 3G and 3Gs screens are different - the physical size is the same but the electronic connectors are not compatible.
In summary : the expensive iPhone screen can be repair kits from iFixit and similar vendors are a total rip-off,you can get the same exact thing for $12 on Amazon.