I'd go for the Fitch
I get the 10kg bags which aren't too huge and to set up a new 100cm cage you'd use about 1/4 to 1/3 of the bag (and then it would be smaller). After that though, the bag lasts me a good six months or more, because with more substrate in the cage to start with, you just need to spot clean/empty the litter tray and don't need to change all the substrate for a couple of months or more (and even then only need to replace about half of it).
The Fitch comes in an oversized plastic bag - so it can be squished into various shapes - to fit under a chair or between a wardrobe and wall eg
It works out a lot cheaper than all the others really.