I recently bought a bale of this from a horse supplies shop - it cost about £9 but I’ve seen it as cheap as £6 in other parts of the country.
Most stable supply shops seem to have it, and you can order online.
The bale is 20kg, but is compacted into a relatively small size for the weight. This is I believe the same stuff as Habistat sell as their hemp substrate.
I’ve tried this with corn snakes, royal pythons and rosy boas, and to be honest haven’t anything bad to say about it.
Its cost effective. The burrowing snakes enjoy it. It has a nice smell. Its light coloured so easy to spot clean, and seems to clump nicely so any soiled parts are easy to remove.
The only downside is 20kg is quite a lot - so if storage is an issue and you don’t need much you might be better buying the Habistat packs. Either way its a great general use substrate.