We spent between $4000-$5000 for our Alaska trip (including air tickets, car rental, lodging, gas, cruise/flightseeing/bear review packages, meals, everything). My friend went to Alaska in May (off peak). She bought a package from greylinealaska.com and spent $3500-$4000 in total, but she didn't do the flightseeing and bear viewing. In one word, Alaska IS EXPENSIVE.
I strongly recommend 26 glacier and kenai fjords cruises, and Mt McKinley flightseeing (which is lifetime experience in my personal opinion). As to bear viewing, I think it's fun and different experience, but it's a bit expensive for that kind of experience.
Hope this helps