Canvas
Canvas can be quite expensive, but you can also make your
own. This requires cotton canvas, for stretchers, and a staple gun with
staples. You will also need stretcher frame keys to tighten a canvas.
If you go to an art store to purchase a canvas you can purchase a canvas
in any price range. At the high end is gallery-wrap canvas, which doesn't
have any of the staples or stretchers showing that are used in making
this item.
If you buy a canvas and then don't have your painting framed, consider
what to do with the edges. There is no rule regarding whether they must
be painted. This is an aesthetic choice left to you as an artist.