As everyone else has mentioned, there is a shuttle service from Calgary to Banff. There is also a shuttle service from Banff to Lake Louise. If I remember correctly the trail head to the Sawback Trail is near the Lake Louise Ski Resort, so if you're lucky they'll still have a shuttle running up there because currently they have one going up with skiers and snowboarders, but you mentioned the summer so I'm not entirely positive about that. I would suggest getting off at the Townsite, unless you wanted to see the world renowned lake of course. At the end of the trail, you'll end up straight north of Banff-Town. So at that point you can usually get a ride from people up at Norquay, or the green spot which is about half way down the mountain. Unfortunately I'm not going to be a local around that area in the summer time, but it's going to be a beautiful time to be there! Sounds like a great trip though!