In comparison to framing, canvas stretching is generally cheaper because there is less expense required in materials. If you stretch the canvas and then wish to apply a frame around the outside then the price will rise accordingly. If you are simply stretching a canvas, then the price is a calculation based on the size of the work and the thickness of the stretcher bars used.
To help give you a general idea we created a quick quote calculator which you can find at the top of this page.