Hmm ... I see your point Paul, but that's from the viewpoint of him selling one set of designs.
If he sells the same set 100 times then he will have made £1,000 for his efforts with no extra work attached. I think a couple of quid would have been a more respectable price to ask, and I certainly wouldn't have paid £10 for them.
However, others may have different opinions and its all about how desperately you need them and how much you are willing to pay.