I paid (I think) $25 for mine last Spring prior to a trip to Oahu and the Big Island. As much as I wanted to use it more, I didn't use it at all on the Big Island. But on Oahu it was well worth it - for those things we would have spent money on anyway. Restaurants and such were the best bargains for us, and all tolled, we saved probably about $100 using the book.
Having said that, I did find it inconvenient sometimes that there were no coupons to use in certain areas, and in some places, (like the Chili's Restaurant in Waikiki), they didn't honor the coupon in the book. So even though we'd have used it more, we couldn't always find a place TO use it.
I'd say if you get it cheap, take it along. One or two lunch meals will pay for the book. If you have to pay full price for it, check the website to see what it has in it before you buy.
Dave