When I got married a couple of years ago we had a john lewis gift list of the standard, cooking stuff, plates, towels etc. put a whole range of stuff at varying prices on. Couldn’t believe how generous many people were.
4 people were absolute stinges though, 2 couples with the best paid jobs of all the guests(one earning a couple of hundred k a year in the city) clubbed together spending about £30 per couple, despite the fact they brought 4 kids with them too. I told the caterers to p!ss in their soup.
We typically spend between 50-100 quid depending on how good friends they are and on what they are after. I’m more inclined to spend more on an actual gift than a cash donation – no logic, just you often see really cool things on gift lists.