This is an example of a non-stretched canvas. They are about 1/2 price of the stretched canvases and I like the casual look of it. I simply folded and nailed this one to the wall, but you can certainly buy a cheap frame or find a cheap painting at a thrift store and nail the canvas to it yourself to save $30-40.
We recently moved and I had a bunch of leftover photos, frames, etc that no longer "fit" in the groupings I had in previous homes. Some of them went into storage until I can use them properly again, but this grouping went together in a hallway based on the color scheme. All of the photos and frames have a large amount of brown in them. Many of the photos have a sepia overlay, and all of the frames are either a light blond wood or a beech colored wood. The small canvas in the middle is color, but the skin tone reflects the blond wood and the darker browns in the photo reflect the beech woods. This canvas is placed near center because it is unique and pulls all of the colors in the grouping together. The entire grouping makes a large rectangle, so it has form and it also serves to camouflage the ugly plastic light switch a bit.
This is a super easy and cheap way of framing kid's art. My kids don't always have a long attention span to makes big pieces of art, but they are able to make many small pieces. I cut card stock into pieces and had my son draw all of the various things we did at Hershey Park. I limited the cardstock colors to 3 and the crayons to 3 colors as well. The look is slightly random, but cohesive and we've got a great framed memory of our child's artwork as well as a great reminder of trips to the park.
Another option when you are looking at wall after wall of blank space, but have little money for artwork, is shelving. I actually picked up a bunch of these white shelves when they were on closeout clearance at Home Depot for a penny each. (These deals are amazing by the way...when they are clearing out stock, you can sometimes by tons of stuff for next to nothing!) To make the shelf display cohesive, I used kraft paper fro the dollar store to wrap books, sprayed a basket white (where I store baby meds), a free giveaway photo album and a 30 cent car from TJMaxx. It was 30 cents because it was missing a wheel, so you can't play with it, but it works perfectly to sit on top of a book and look cute! :)
...the other option is to pull paint off the wall to make modern art...at least that's what my 2 year old things :)