Not sure why you are comparing what a person wears to the cost of a laptop. Sarah Brown's clothes are not paid for by the tax payer (as far as I know).
If you took another person whose husband earned a 6 figure salary, and it was a very important day for them both, I think you will find that her clothes were very cheap in comparison.
I tend to wear expensive suits as opposed to cheap ones. I have friends who buy from Greenwoods - I tend to buy from 'proper' outfitters. It is my choice what to wear.
Why not pick on Gordon Brown's car, and say that he could drive around in a skoda instead of a limo?
Or point out that he doesn't need Chequers etc etc
Personally, I think you are just being a jealous woman!