What one you going to Lord Flynn - Lanark? cages I think are about £6 for the big (they are on the floor and open from the top, for lots of hens or geese/ducks) or the smaller you could get away with (front opening) which are off the floor like the usual pens at poultry show - think they're about £4. But take into account your diesel getting their and your time and you have to think if it's worth it (rarely it is unless you're into big numbers like VF). I do it occasionally as I don't get out much.
Like VF says, its a good idea to put in a chunk of iceberg lettuce or such like and a wee dish of water so they look like they are from a caring owner

and I usually put a little card which says very briefly how old they are, when they were wormed last and colour of eggs, what you normally feed them, if they are used to being housed or free range. It shows quality stock.
Hopefully that way they will get someone equally as caring as you