Can anyone tell me how much this book is worth?

The key question to ask is if the book is a first edition, first PRINTING of the story. Without knowing that, it would be hard to gauge how much your book may be sold for. But in any case, there is a bookseller who is selling the same story but without illustrations for $60. With illustrations may garner another $10 or $20, if you're lucky. If you sell it, don't expect too much for it. Do a search on froogle.com or eBay, and it looks like there isn't that much of a demand for it.