What strikes me, more than the amount of money involved, is that he read you a text from his wife, as though she has the last word.
Does he make a habit of this? Is he using her as some sort of benchmark for you to live up to? If so, I understand your discomfort.
I'm not suggesting that you both pretend that she doesn't exist, and she is the mother of his son, so the fact that they are sending a joint present, while odd (IMO), needn't necessarily be worth getting upset over. It would annoy me, however, if after I had expressed an opinion about something, someone else's opinion (probably particularly an ex-wife's opinion) was used to 'trump' mine. There was no need for him to read out her text, and I would be unhappy if this sort of thing happened on anything like a regular basis.