I own two books that I purchased while in the USA and I have to agree with Randy on the state of the market, well ebay anyway.

All I have found these books good for is identification of various models and found it in no way helpful at all for gauging value.

The Standard Guide to razors is supposed to be for calculating value, i havent worked it out as its an individual thing.
The other is a book called 1000 razors, its great for looking at ones youve never heard of.

At the end of the day the price is whatever your willing to pay.

Just my opinion and feel free to disagree with me.

Cheers,simon