I don't know if I was lucky, but there was never any feeling that I need worry about parity with the inlaws. As I said earlier, I don't know how much they contributed, and though I dare say they knew I was buying the dress, I don't imagine that my daughter will have talked cost with them.
I've just remembered that at the last minute I contributed sommething else - and this also can be a way to go. The wedding meal was quite late in the afternoon, people had travelled a fair way, and I was concerned that they might get really hungry.
There was quite a gap between the ceremony and the meal, when drinks were provided - but the couple it turned out, had economised by not having the canapes that the venue would normally provide.
When I found out, a few days before, I called the hotel to find out the price, checked that there was enough time for them to arrange it, then contacted my daughter and offered to pay so that people could have a bite to eat. That made me feel a bit better about the guests being treated thoughtfully, and the couple were very appreciative.
Anyway, that's something you could always consider. Wait until they start planning, then see if something crops up that they'd like but can't run to.