Lets do the math Lew. You've already decided you'll be in St. Louis. We all know the blender is coming with you, this dictates you'll be bringing the truck. You can't put that smelly thing in your wifes car (I'm assuming it gets the better mileage)
Since you know you'll be there, much of the travel cost is already sunk. You just need to look at incremental costs. Those are entry fees and fuel. I'm sure your truck gets about 16 mpg on the highway so the incremental is only half of your 8 mpg*3000 mile statement.
Fuel for the cobra is almost negligable being a smallblock so I'm not considering that.
I'll even bring the tequilla and fuel for the blender if it helps.
See you there.
Mat