.. as others have said check around for financing then do a numbers comparison (i.e. interest rate savings vs. trunk money) and decide.
Now if you are going for the trunk money .. I think you can get the overall price down a bit more. So subtract $3500 from the car's INVOICE price (i.e. base INVOICE + options INVOICE). This number is the dealer's INVOICE .. ! Add around $300-$500 (dealer profit) and the GGT ($1500) and you should be good to go.