Local "self storage", or alternatives

In my spare time, I do a bit of modelling... railways, that is.

Being, as I am, a flat dweller with minimal space I took the decision to build my layout on a modular basis with a future move in mind - this is grand but of course does rather restrict what I can do as they take up a lot of space!

I've looked into the local branches of the well known firms but they're all pretty expensive (£15pw for a space the size of a phone box is about par...)

I was wondering if there are alternatives locally? Clearly I would require a dry (and preferably dark) secure space where fragile items could be without interference, with fairly regular access - is anyone aware of anything?

Cheers!