I actually thought the paying for Xmas dinner was a joke!!
Do grown ups kids not chip in/buy something for the dinner at their parents? In My family, me and my siblings will buy the chocolate, biscuits, boxes of sweets etc and maybe the veg. Other family that come will buy a big ham, my parents will buy the Turkey and the rest of the bits. People will also bring cake, pudding, trifle, wine and beer etc.
This is a much nicer way to do it (and not expect the poor parents or whoever who are hosting to provide everything too) without actually getting people to hand over a fiver per head, that’s just bizarre!