I have been to Alaska many times and would throw out the suggestion of doing your own land tour instead of an organized tour. For me, this is the best way to go. Renting a car and driving in Alaska is very easy and very enjoyable. Some of the reasons for going on your own are that you can go and do what you want, when you want to. The overall cost will be significantly less than an organized tour, especially if you take advantage of the many 2 for one offers found in the Alaskan toursaver coupon book.
If you do want to consider this option the one thing to know is that Lodging can be many miles apart and making reservation is a must when traveling in Alaska.
If you have any questions, please ask.