In reply to Dominicandave:
Depends where you are of course but there are often other options that aren't the big storage companies. I found locally a farmer with a barn full of shipping containers (I actually wanted a workshop rather than storage) with power for not a lot of money, I forget how much but maybe £100/month for a 40ft container including electricity.
You could try looking/asking on gumtree for garage space.
jk