I'm also upgrading from a 450D - and decided to go with the 5D mk II. You can get one refurbished or used for a little more than the 7D. On amazon the 7D is about $1600 right now, in the Canon refurbished store the 5DII is $1760. Of course you can find a used/refurbished 7D even cheaper though.A Canon refurb 5D2 at the Canon Refurb store is $1760 + tax & shipping and a Canon [7D] refurb on the Canon Loyalty Program is $1087 + tax, no shipping last I looked. That comes out to about $690. That goes a good way to getting a nice lens.
Edit: Canon 7D is $1087