Costs are high during summer -- typically triple the price for hotel rooms and rental cars compared to December -- can't imagine why! (my own ANC story is renting a car in December and finding the doors completely frozen shut, not just the lock but the whole door). Despite the cost I would say renting a car is mandatory if you want to see any of the good parts of Alaska. The alternative as mentioned is the railway to Seward and a cruise (which, if same cost as a rental car, might be a good option). Save elsewhere on your OWE trip, in ANC you have to spend money and you have to leave the tourist strip in ANC (which is abysmal).