The ship tours to Mendenhall run about $40. I just did a tour by Mendenhall Glacier Transport for $20. This was purchased on the pier, they will have people waiting as you get off to sell tickets and had several departure times. You travel on an old school bus instead of a full size one but are saving $$. Other option is to take the regular Juneau city bus for $1.25 each way but this drops you off about 1 1/2 miles from the visitor center. If it's a nice day and you don't mind walking this is cheap option.
Juneau is also in my opionion the place to do your flightseeing.
Check out my reveview of my recent trip on the HAL Statendam at www.cruise-addict.com
in the review section.