spose that depends where you are,
I'm in Kirklees (up north) and I have 2 garage plots, one with a garage and one without, they cost me £40 apiece annually. The prices are increasing at 9% until 2007( or 8) then inflation linked thereafter. I do have the extra cost of actually putting a structure on them, but cheapo 2nd hand concrete sectional gages can be had for £150.
I've got them until I no longer want them, or the council want them back. (They could decide to put housing on them I suppose, bu I think the ones I have are pretty safe). If I ever want rid of the plots, I have to remove the structures, in practice though I'd just sell the structures in place to the next tennant.
As a comparison, we where paying £120 a month for a private Lockup used as a domestic garage. It would fit 4 cars and still have some space to work. We had it for a couple of years, but the council suddenly decided we should be paying business rate tax on it and wanted about £2000 in back tax. We got them to wiave the back tax, as we where originally told it was exempt, but they then want £800 a year in tax, so we packed it in.