what are cheap ways to make picture frames?

tree branches

cardboard.

Use lolly sticks to make a square or you can glue some twigs into the right shape for your frame for a rustic look

Try using a hot glue gun or if you don't have that some type of strong glue and use different sized sticks from the garden or wherever, I have done this and bought some fairy lights to wrap around it and put it on the wall of lean it against something, turned out really nice. Could even cut out a cardboard cereal box, cut it into the shape you want and glue the edges around the bottom and sides (leaving the top open for the photo) and cover the cardboard with buttons maybe or leafs, glitter, whatever. That sounds pretty cheap to me...but even shopping at second-hand stores and buying frames, you can paint them.