Storage heaters are pretty simple things.Basically a short length of flex some controls and either 1 2 3 or 4 elements.
If its Dimplex or Creda all the parts are available (not from B&Q etc though....from a wholesaler or specialist or the web).
An element is around £30 so are the controls.
I would not recommend DIY you need an electrician.
At a guess worst case £100.
Regards
Steve
Steve, March 2008