As a farmer dealer for Syngenta, you should know the triple stacks (corn bore, root worm, ect) will only improve your yeild if you have pressure against these insects. The key thing to look for is a good base genetics (refuge) and buy the add on's accordingly.
As far as the cost of the seed ther are alot of variables in there, volume, early pay, types of genitcs.... All these play a roll in your overall cost. In my dealership I would guess the average is somewhere in the $180-$200/per bag range. Most of these are 111 day.