This is really frugal and almost free, but definitely an Xmas money saver- don't throw away all those outer leaves when you trim up the sprouts for Christmas dinner - make some soup, I tried it today for lunch - it's delicious and cheap! It may not sound great but I don't think even sprout haters would realise what it's made from!
You could even make it with left over sprouts if you reduced the cooking time a bit - and save even more money.
Here's where I found the recipe!