You don't need any money to start a dog walking business. This book tells you how for $5.99. The start up costs are literally zero. It would be helpful if you had a car and some sneakers, but neither are necessary.
A dog walking business is fun and athletic. A better cure for depression cannot be found anywhere. The sun and the exercise, not to mention the interaction with the dogs and cats, will pull you out of your funk in no time. It even helps with PTSD - trust me on that one.
The $5 book The Dog Walker's Handbook describes everything you need to know to run a profitable and fun dog walking business. It's perfect if you are totally broke, as I was when I started, since you don't need any money to start earning money right now.