We are taking a river cruise from Budapest to Amsterdam. We thought we would like to visit London as we've never been before then go home from there . What is the easiest, most cost efficient way to go from Amsterdam to London.? Doing a Fodor search there is talk of a night ferry which isn't appealing . Also train to Brussels and then Eurostar to London. Any advice regarding this would be welcomed.

Flying or Thalys/Eurostar are your options.
You can get good deals on either if you book early enough.

I note that Brugge is on your wishlist. Consider taking train to Brugge via Brussels, spend a night or so, return to Brussels to take Eurostar to London.

Central station in Amsterdam can easily be walked to from the docks - provided your luggage isn't rxcessive. If "we" is two of you I would consider 2 carryons plus a larger case OK. We did it and my wife walks with a cane.

I'm no expert, but I flew between the two cities. They aren't exactly close.

Fly from Amsterdam to London City Airport (LCY). Both BA and Air France/CityJet fly the route.