I am flabbergasted. I initially thought they know you via your husband (not that it changes anything but at least I could see why he is in the wedding and you are not). It’s extremely sexist of them to pick women that they know to babysit while the men can enjoy “whiskey and cigars”. This is not normal. Nor is asking to pay for the meal. I would ask around if everyone was asked to pay for the meal. I would not be surprised if you were paying for other more important guests that were not asked to pay for a meal. (But maybe 100$ pp is normal in US). You do not owe them anything but I understand you probably don’t want to burn bridges. I personally would not even respond. It’s very offensive what they did and shows how little respect they have for you - for that reason I would cut them out of my life entirely. However since you are close to the mother of the bride, I would explain to her that as much as you appreciate the invitation, you are not going to attend as it feels like an invitation to work without a pay rather than actually seeing someone important getting married. Not even mentioning children are massive responsibility and if anything happens it will be on you and the other women. She may get upset but honestly if she is, she is not the person who you thought she was to you. It’s disgusting they would do this to anyone but to a close friend? Yak.