I don't think it is too bad a price, I would have paid that for one new one a couple of months ago if I had the money then. There might be a few more sets coming out of the woodwork though, I got a letter in practical classics this month highlighting how hard they have become to find, assume this set appearing could be to do with that. The more that appear, the cheaper they should get.
I think £30 is the least I would expect to pay for a new unit for any car.