Though this book is old (now.. I write this 2011) and there have been a number of new species described (hundreds, actually), corrections and revisions, it has been (until perhaps this year) THE bible on aloes. It is woefully lacking in illustrations and those it has are fairly poor in quality. And it is one of these annoying scientificly organized monographs that do not try to make themselves user-friendly by listing species in alphabetical order (so the index page gets over-used as is the first part of the book to wear out). It is a useful book, however, in trying to win arguements and to find out geographical information. It has little or no cultivational suggestions and its descriptions are definitely geared toward the literate botanist and not the back yard aloe fancier with a degree in art history.
I have no idea what this book used to cost (that information was cleverly snipped off the jacket on my copy) but it is very hard to find nowadays and volumes run anywhere from $100 and up (seen some for over $200). I am sure the original price was far less.
It has no IBSN number and was printed and published in South AFrica, so am not sure how it was promoted or distributed.