What time of year are you going???
If it's not the busy season, then you can get rental cars really cheap!! AK is great, but you have to bus to get anywhere, so I would totally get a rental car for the entire week.
We get the smallest, cheapest car that we can, and then use ME to transport our luggage.
Not sure if you are doing the dining plan or not, but another great thing about having a rental car is being able to eat off site for 1/3 of the price! Not saying you have to eat off-site every day, but it's definitely a nice option, and the $$ you save will cover the cost of the rental car.