Blimey, what kind of weddings have you been going to?
That amount is seen as the minimum cash gift in cities for wedding , in the countryside it is seen as generous. I went to a wedding last year in Warsaw and the couple received a lot of money. As a 2+2 we gave the going rate, but many people gave significantly more and they were not blood family.
I like the idea of gifting money to a charity, but lets face it when you are staring out as a young married couple, you need a leg up.
As far as the OP is concerned, I would book a sunday Brunch for the couple at one of the 5*'s and forget the flowers. As any person that has been to a Polish wedding knows, they have flowers coming out of their kazoo by the end of the day ( flowers are a waste of money, except when you get that guilty feeling)