It is possible to load the car and return to Anchorage via Achemak bay

Look on Groupon they almost always have a special that can save you some serious money. Groupon.com select Anchorage, Ak. There's no cost to join so it's real savings.

If I understand this correctly, you can rent a car in Anchorage and drive to Seward, then select from several different tour boats that go out in Kenai Fjords. But not Kachemak Bay. You drive to Homer for that.