I don't think the should be a recommended amount supermick as it is so very personal and also depends on state of finances etc,whatever it is one decides will and should be gratefully received.
We give £50 to nephews and nieces if that helps - a son is a different matter, and it would depend on circumstances - whether or not they already have a house, etc. Nobody's ever given me £10K as a wedding present - we paid for our own wedding.