Apparently there is now a 3rd option for GRO records. They have now got a digital image option for only £2.50. It is only available for Births from 1837 until 100 years ago, and Deaths from 1837-1887. Not tried it yet, but it is cheap!
Kevin, thanks for that. it is a major step forward in cost reduction for those older records.
The site does warn that it is possible some records may not be available as the digital image so I guess we must just suck it and see.