If each tire in the front of the car cost $12.40 more than the rear tires, then the total would be $24.80. And because we say that each tire for Luke's race tire is going to cost him $100 each, he would be paying $224.80 for the two front tires, while including both the cost of each tire and the additional 12.40.
This is hard to answer since I haven’t been through this situation, but I do recommend having a calm serious talk about your feelings, if he sees how serious and passionate you are about this, he may consider giving it a go.