Collage is lots of fun, and inexpensive.
All you need are posterboards, masonite, or other stiff board to use as your background, and something to glue to them ... for example: Pictures and/or words you like, clipped from some magazines, newspapers, junk mail, and greeting cards, old calendars, old maps, and embellishments like buttons, feathers, rhinestones, used postage stamps, neat bits of broken jewelry or parts from old clocks, telephones, etc. (Disassemble any old, broken mechanical or electrical things and save the interesting pieces!)
Cover your work surface with newspapers to help keep it clean, place the poster board in the center. Pick out your favorites of all these things, arrange them loosely on the poster board. When you have an arrangement that is pleasing to you, start carefully gluing them down. I like to use Elmer's or another white glue that has been thinned out with a little water. Smooth out the pieces to get out all the excess glue and any air bubbles. Get it where you want it the first time, because it's VERY hard to reposition anything ... sometimes, impossible! Put your embellishments on last using the glue full strength. (Try to avoid getting the poster board too wet. You don't want it to curl as it dries. If it does, once it is totally dry, place it under stacks of books or bricks, etc. to flatten it out. Leave it there for a week or so until it flattens out.)