really wouldnt bother with any wax from Halfords, some stock the Autoglym HD wax, but charge £40 for it. You can get it off ebay for almost half that.
I would personally go for something from the Dodo range for around £30 or perhaps one of the Poorboys Nattys range (blue is my fave due to the smell

) for around £15, or Collinite 476s, which is not as easy to use as Dodo or Poorboys but last twice as long, again for around £15.
I use Halfords for picking up cloths etc, or similar priced Autoglym stuff (can rate Fastglass & Bumpercare)
hth,
cheers,
Chris