My daughter's classmate's father bought a dress for my daughter. How can I say thank you?

Your daughter's classmate's father bought a dress for your daughter. To show your gratitude, you can say, "Thank you very much for spending so much money. Your eyes are fine. The dress you bought is very beautiful and fits well. We all like it very much. " However, this situation is very embarrassing. After all, he is not a relative or a friend. Do not accept! It's hard to be compassionate, so accept it! I feel as if I owe him a favor. You'd better give his daughter a gift in return, or invite them to have dinner together.