Book
There have been some other posts somewhat related to books on another thread. Other casting books (Author/ dealer prices) out there are Speycasting (Falkus /$250+), Speyfishing (Maxwell/$110), Fine and Far Off (Scott/$100- $150).
Not to diminish the previous authors, as I like all of the books and they have value for different reasons, but I agree with recommonding Simon's book in terms of content for casting (independent of price); there really is no contest. Additionally, as it was just published this year, it is easy to obtain at reasonable prices.
As a suggestion, put it on your list to Santa this year instead of waiting ten years and paying 10X the cost - it is much easier this way. Given the assumption that you will purchase Simon's book, and I think I would pick Fine and Far Off next.