What do you think about me paying a lot of money to go to a music fest that I don't even want to go to?
Really? Why would you pay for it if you don't want to do?
My friend Jimmy said he would go if I paid $403.
You should not have to pay to do something you do not want to do. It is wrong for your friend to expect such a large  payment.
Jimmy made a mistake and now I feel obligated to buy the ticket.
You don't have to pay for your friends mistake, and he shouldn't expect you to if he's a real friend. You should speak up and let him know that you don't want to go.