I'm referring to the contract with the caterer, and possibly with the local wat who provide the monks for the chanting (I don't know if that falls under Thai commercial law, but I think not). I presume your wife depends on your support, so she has a right to comment on how you spend your money, unless ฿500,000 is a trivial amount to you. If you're married in Thailand, by the way, the money is half hers, not yours alone.