I would be extremely pissed at this!!
It reminds me of an old colleague in the pub once. Everyone got rounds in, then when it was his turn he just went and bought for himself.
If you feel that strongly about it, you should say something. Put it in a letter. Sounds official (!) but it's not meant to be. It means you can tread carefully when choosing your words. The letter can be edited before giving to the MIL.
Otherwise, as Bungo said, chalk it down to experience. Once bitten, twice shy.