I would recommend you to sell the grip and body and lens separately.
The new 17-85mm lens itself cost like 1K, which u may sell it to most of the kit I owners, they will be very interested for the upgrade (longer zoom range, IS, USM, ... ). You may grab an offer around 600 - 800.
The battery grip can be easily sold at the price of 110 - 150, it's popular. (the original price aroudn 250).
The camera body??!! Not very sure, but can easily make it 500 at least.
So, u do the calculation urself then.
Good luck selling!
Btw, why r u selling the kit? I am owning the same kit as u and perfectly satisfied with it. If u want to give up shooting, good for you! If you intend to sell it and buy the 450D coming out, u better think it again!