The Stonehenge book was £80 when it came out and has never been remaindered or reduced to my knowledge, and as this book is ten years old that was a hefty sum in 1995.
The thing about that particular tome (which weighs as much as a dumbell), is that EH attempted to use it as an excuse for not having told punters entering the site that the stones were re-arranged and plonked in concrete - or in other words they were saying that the information was in the public domain and so they didn't have to put that information in the everyday pamphlet guides and the talking guides or the information boards - the fact that "the public" don't go near tomes of that size or price was something they ignored. This is their trick with Silbury of course, they tell the public zero about it then will point to some report tucked away somewhere and say see the public were told.
As for Avebury Reconsiderd by Peter Ucko et. If you see one second hand grab it, as it is rarer than Whittle's Silbury rings. Only do make sure it has all the seperate maps and clear slides with it - I saw one for £60 recently and it had none of the attachments and still sold. Someone has stolen the slides from all the public libraries within distance of Avebury so you can't even get copies of them.
VBB