It all depends on what size your work is. Everyone is giving great advice! I used to work in a frame shop, so I do a lot of my own framing. If cost is an issue, sometimes I go to Goodwill or other thrift/second hand stores to buy used frames, and then I paint them. I do that a lot actually. They usually turn out pretty nice. Also, if I'm not working with stretched canvas, I always make sure my work is a standard size, or that it can be matted to a standard size. Custom framing can get super expensive! Good luck!
Depends on the size of the canvas. If it's a standard size you can pick up frames just about anywhere. If it's custom, you'll need to go to a frame or craft store and have them cut them for you, or make one yourself.
The cheap frames don't have glass, but they might have a clear plastic film that looks like glass. You don't need to use that, just the frame. Don't buy the thin black frames because you can't see if the corner is broken until after you buy it, and when one is broken then all the same size is broken in the same place.
I stretch my work on stretcher bars for the most part. But when I do need a frame, especially for a canvas that has odd dimensions, I'll get a larger frame at walmart, and cut matte board to fit, then cut a window in the matte board for the original artwork to show through. Usually art stores will cut the window matte for you at no extra cost (when you buy the matte board from them), and the walmart frames are always much less expensive than custom framing. You can take out the glass if you don't like it.