Sandy Bridge CPUs in general are much cheaper than the upper levels of the i7-900 series. They are a considerably better bang for the buck.
You might consider avoiding the Sandy Bridge processors with the K suffix if you are not overclocking. They are designed for overclockers and you pay a bit extra for the privilege.
The 2600 is considerably more expensive than the 2500 and you might consider saving that money and applying it to something else--an SSD, a better monitor, etc.
I think Intel will be releasing more Sandy Bridge processors shortly--some of them designed to use very little power.
I upgraded to a 2500 a month ago with no regrets. The graphics capability is built into the processor and works well for my purposes (WEI graphics score of 5.1; gaming graphics 5.8; but I don't game). Power consumption at idle is 80 watts, down from 115 on my previous Core 2 Duo E6600.