I don't drive. I think I've driven twice since I got my license 12 years ago. I have resisted getting a car for a variety of reasons -- they cost too much, they're scary (if we put half the money into reducing traffic accidents as we do taking sewing scissors from air passengers, so many lives would be saved...), and not least it's difficult to go from having one to not having one. Since I've never had one, I'm used to it.
If you have to carry that much stuff with you, there is a good chance you'll stop commuting by bus. I probably would.
Is there a way you can consolidate? Get a locker in the gym or go with a friend who can keep it in their car or carry less? I carry a nice leather backpack; it cost less than $150, looks professional enough, I can carry a lot without hurting my back, it holds my laptop and books and lunch, etc., and I don't need a car to store stuff.
Find something to do to make the bus ride enjoyable and/or. I read a lot, or write, or meditate. Some people knit or do other handwork. Have a cell phone and a city map. Or a cell phone with map access! Both are very helpful. Know your bus schedules and see if they have a scheduling utility online.
When you do your cost analysis (not something I can help with, since I don't have a vehicle at all), see if you can take some taxis sometimes. It's a relief to know it won't blow your budget if you get stuck somewhere. My local metro has a "guaranteed ride home" program, which will reimburse you four cab fares per year if you commute a certain percentage of the time. For the difference in price between having a car and not, well, put it this way. According to Quicken, I have spent $366 on transportation so far in 2008.
It might help to put the money you save into a special account. Watching it grow can be a great incentive.