B.F.
Wow, I bet you will get a lot of ideas from moms who aren't so lucky to have that much free time!
Library, book store, craft store, yard sales/flea markets. Gardening, volunteer somewhere, take a class, do some sightseeing in your area, poke around an antique shop...
Tried to think of things that were cheap/free for ya. I think you just need to search for something that interests you and go for it! Most likely, you'll make some new friends, and then you can spend time with them!
Good luck!