I don’t see a problem with asking for/giving money.
When we lived in Hongkong we went to several Chinese weddings and the custom
was to give ‘lucky money’ in a special red packet. Very sensible in my view.
If a couple request money instead of a gift, I heave a sigh of relief that I won’t have to wade through a list hoping there will be something suitable left on it, and I just think of it as payment for the occasion - the meal and the party so I think £80 - 100 is appropriate, perhaps more if it’s very lavish.
When one of my young relatives got married last year the invitation included overnight accommodation and breakfast the next day at the venue, so our gift included a sum of money to reflect the fact that we hadn’t had to stay overnight in a hotel.