I heartily agree that dogs add much to one’s life, but they are not a low cost hobby. Food costs, perhaps not so much for a small dog, but proper vet care can add up and dogs require care and attention for their entire lifespan, which is a major commitment, unlike other hobbies that can be picked up and put away when you get tired of them.
On the other hand, perhaps there is a neighbour’s dog that would enjoy going for long walks with you. No expense, and dogs can be lovely walking companions.
That’s exactly how I feel about it.
Walking without a dog almost feels criminal.
I see dogless people walking and think that’s a waste of perfectly good walking.
My latest hobby has been going to estate sales. It’s sort of like combining thrifting with houseviewing.
Estate sales have much better stuff than you will find at thrift stores or at garage sales, and there’s a lot more than what garage sales have. They also tend to run longer than garage sales - two days at least, and 6 or more hours for most of the days.
Plus, you get to go into the houses, without some salesperson trailing around trying to sell you every other step. I’ve been everywhere from some of the ritziest neighborhoods in the metroplex to poorer houses, to hippie apartments. For someone my age (50) these houses are often a trip down the memory lane of all the different decorating trends. The best are the hoarder’s houses - wall to wall stuff, and that’s after the estate sale people cleaned out the actual trash.
These are also good sales to go to if you want to do upcycling. They are also a good wake-up call as to just how much stuff people tend to accumulate while they’re alive.
The only downside I’ve run into is that my husband has taken up collecting cookbooks. We may have to rent a booth at a flea market one of these weekends.
You would enjoy this if you like shopping, seeing how other people live, or snarking at other people’s taste. 
ETA: estatesales.net is a good place to look for sales in the U.S. and Canada. Craigslist & the local newspaper are other options.
Don’t know what you can do until you try! 
It’s funny that you say that since you are a talented quilter! I tried quilting and found it to be far too tedious for me. Different strokes and all that.
Be a volunteer or docent at a local museum or historical society. It will cost gas to get there, but maybe if you live in a big city you can take public transit. At the museum where I volunteer, they had five free Saturday morning training sessions where experts in local history and 19th century architecture, costuming and society lectured. It was like attending a free college seminar!
The other volunteers I work with are all fascinated by history and many have unique and specialized knowledge and experience. The museum has a historical materials library that we can use for research.
There are always jobs to do- leading tours, helping set up for special events, creating training and learning materials, easy manual labor maintaining and restoring things, etc. I’m developing my public speaking skills by leading tours.
Every tour I lead someone says “wow I never knew all this stuff was here”- you’ll get people in your community more involved in their history and social context.
Nothing makes time fly like a live all-nude lesbian sex show.
I play Jazz music on the side…it’s always nice to be paid for your hobby!
Our County animal shelter lets folks walk the dogs that they have.
I forgot to mention my hobby, actually, which is standup comedy.
If I lived right in Toronto, it would be extremely low cost. As I live a 40-minute drive away it unfortunately is not. But the performing arts can be a great hobby and pretty cheap to get into.
Thanks for the coursera.com recommendation - I’m signed up for a class on quantum physics starting in March!
Wouldn’t negative cost be even better than low cost? I’ve started doing crafts and artwork… and selling it. And, no, I’m not that talented.
Just want to say that with a wife and two kids and a confirmation class and a scout troop and a job, I’m jealous.
Go to Khan institute and get some studying in. You never if what you learn there will take you someplace new and exciting, even if in your own head.