and as long as they have the knowledge and equipment to do it without killing themselves, but it is definitely the cheapest option, which was the question.
if you have an aerial already and you have a good analogue reception try a digi box first it should be fine don't be pushed by tv people telling you need a digi aerial, no such thing an aerial is an aerial, of course if the digi box has poor reception then by all means get a new higher strength one