Actually, the 5dII kit (w/ 24-105) has gone as low as $2400 or so; but its more regular to find it in the $2600 range.
But, yes, your math makes sense, it just depends on what you are willing to spend on. The 5dII I believe is now 10% off through Canon Loyalty, which makes it $1580+tax. So, probably $1650-1700 after tax. And its pretty easy to find someone selling the 24-105 new out of their kit for $800 or so. But, that leaves you at $2500 with a 90 day warranty on your camera, and no warranty on your lens.
So, if you think you'll want the 24-105 for the camera, I'd get the kit, as for that extra little money, you'll have a 1yr warranty on everything