I'm not sure if this is a cultural thing, but I'm not offended by the couple asking for money (I write this from the perspective of someone who got 13 Teapots and 5 Slow Cookers amongst her gifts 35 years ago, lol. Most of them I gave as presents to other people when they got married!).
What does offend me however, is people who state that "Your presence is enough, BUT if you'd like to buy us a gift..." and then include a gift list or registry. Too hypocritical for my taste - if you're hoping for a present, then say so - don't pretend you'd really be happy if guests arrived empty handed!
I think your neighbours are being just that - neighbourly by inviting you.
Just because they've asked for money, doesn't mean you're obliged to give any. You can, if you wish, give them something you've made, or something you want to give.