Photographic books seem to be strange things on e-bay. I have the Rotary Process Manual by John Tinsley. It seems a very ordinary book although the info is good but that went for over £33 on e-bay. The common link here may be books out of print and which were regarded as a classic on their subject.
I couldn't see any copies of John Blakemore's B&W Workshop by e-bay sellers, including the specialist Powersellers for less than about £8/9 but then found it on Amazon for £1.99!
I'd be wary of books on e-bay. If they can't be had for love nor money elsewhere then you pays the rate but for some reason photographic books on e-bay seem able to exploit a market where supply and demand do not conspire to produce the lowest price.
As recommended here on APUG I will in the future check Amazon first every time.
pentaxuser