Cheap or free mosaic. Made this one in a few hours, including drying time.

Step 1: Materials

Scissors
Big puzzle
Big piece of cardboard
Elmer's glue
Spray paint
Picture
Pen or pencil

The cardboard should be really big, so that you can more easily tell what the picture is. The puzzle should also be very big, to cover the big cardboard. I think it would be about 160 puzzle pieces per square foot.

Step 2: Embiggen

Choose an image with few colors, and then embiggen it on to your cardboard. You can do this many ways, such as putting a grid over your chosen image and then a grid on the cardboard (example), or using a projector.

Step 3: Seperate

Separate the puzzle pieces into however many different colors you need. I used tan pieces and the backs of the pieces (bluish-green) as two colors. I painted other pieces for the black ones (next step).

Step 4: Background

Glue down all the pieces that will be the same color as the background. For example, on mine, I put down all the black parts first. Then use the spray paint to spray the whole thing. This may take a few coats. You can use scissors to cut pieces for the edges if you want.