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I get 70 litre bags of fitch

It's recycled food grade paper bedding. My hamsters love it and I've been using it for years. It's not as soft as kaytee clean and cosy, but it's fine

A 70 litre back will give about 8" deep substrate in a 100cm cage and probably over 6" deep in a 120 cm cage. If you already have bedding in the cage, then a 70 litre bag will last quite a long time, and it's not too big to store really.
Fitch via Amazon
Or you can buy it directly from Fitch First where it shows as less expensive, but once you add the postage I think it costs the same.
Actually it costs a bit more buying it direct from Fitch First, I just checked. With delivery costs it came up as £38.98. So it's a bit cheaper from Amazon and it's also one of our Amazon affiliate links, so the forum gets a small commission

From Amazon it's showing as £36.09 for me and £37.99 one time purchase with delivery. So it's not a lot different in price really.