We have opted to DIY before a cruise leaving out of Seward. We feel we can see more of what we want in that time. We plan to arrive in Anchorage, rent a car and spend the night there. We will then drive to a hotel near Denali and stay either 3 or 4 nights to see Denali. We do plan to do the long bus trip into Denali one day and will plan what else to see. We will then drive to Seward and spend 2 nights pre-cruise there. In Seward, we plan to do a day cruise into the Kenai Fjords. Depending on time, we might also see the Sealife Center in Seward. We found that Hertz will rent cars in Anchorage that you can return in Seward. I am not sure it will save much money, but we can do things on our own and see the scenery and wildlife on our own time.Sounds like a wonderful trip! I'm sure you'll enjoy every moment.
The Denali Chamber has a list of lodging choices if you need some ideas: http://www.alaskaone.com/_dcc/accommodations/
A couple of hints about a rental car .... rates change frequently and since Hertz is the only vendor in Seward, grab the best price you can find now, then check back weekly for a price drop. Even up to the day before you leave, keep checking.
If you find the drop off fee is too high (often $250) keep in mind that you don't NEED a car in Seward, so price a RT car rental for 5 days, and the train to Seward. May work out cheaper. Plus I've read that train segment is supposed to be the most scenic. Seward has provided a shuttle bus around town for the last few yrs, and a taxi in town is $5-$7. If you want to visit Exit Glacier there's a shuttle for $10pp. And there's a waterfront trail that leads from the harbor to downtown (SeaLife Center) which is about 1 1/2 miles. During the walk you can watch otters playing off shore, bald eagles, lots of fishing boats, and wonderful views across the bay to the mountains and glaciers. Hope this helps. Have a great trip !