I purcahased mine from U.K. and even w/shipping it was much less than anything similar on (U.S.) ebay.
Whether it's worth it depends on how serious you are about the Lambeth style of decorating (although it does contain recipes, also) whether you're a book collector or if want the ultimate gift for a cake decorator. Suppose resale (either after reading) or as primary goal is another option.
How much you pay also depends on the edition and conditon of the book. A signed book is also more valuable.
Here's a link which details standardized book grading criteria: www.ioba.org/desc.html
If you're patient, "readable" copies do become available on ebay which are significantly less pricey.
If you have time to spend hunting and searching, certainly yards sales, etc. might pay off with a steal of a copy.
How much time do you have, and what is your time worth?
FYI, the vintage Wilton contour (bevel) pans that complement this style of decorating are also seen on ebay from time to time and can end up in $$$ price range.
Some of the older Wilton decorating books are also hotly traded items on ebay and other book sellers.