Here is a video I made about the panel boards I use to paint on. It's very economical and the boards are very nice to work with. One advantage in using masonite boards is they don't take up very much space which is great when traveling or plein air painting.
Be sure to cut most of your boards in standard sizes as frames are much less expensive to purchase that way. Many frame shops cut their scraps into standard sizes and sell them cheap. You can end up with great frames for a fraction of the cost.