The train to Denali leaves Anchorage at 8 in the morning and takes 8 hours. You need a full day to see anything of the park, so counting the train ride back, you'd have to leave on the morning of the 27th and come back on the 28th, as returning on the 29th would make you miss your plane. Besides which, it's pretty unlikely you'd be able to find lodgings that are remotely affordable close to the park. So in my opinion, Denali is simply out.

Without knowing what deals and arrangements the cruise lines might offer, you can ride a bus from Whittier the morning your cruise ends for around $70 per person (maybe cheaper if you take the cruiseline's transfer) and rent a car when you get to Anchorage. 3 days rental at ANC will run around $350, so you're looking at ca. $500 for bus+car for 2 pax.

Or there's a train that will take you to Anchorage in the evening that's ca. $10 more per person (again, maybe different using cruise transfers) but would save a day's car rental, so maybe ca. $350 all in for that option. Spending the day in Whittier would allow you to take a glacier cruise as mentioned above.