I buy the "Oops" paint at Lowes to use when I redo various pieces of furniture. I bought an old baby changing table for $5.00. I mixed a couple of the small paint containers and got a lovely light lilac.
This page contains the following solutions.
"Oops Paint" is what the home improvement stores call the paints that were tinted incorrectly and the original purchaser was unhappy with the color. You can generally get a gallon for anywhere from $3-5. Check in the clearance area or ask at the paint counter.
When going to repaint a room, go to the oops pile at most home improvement stores. These are paints that were mixed but didn't sell.
I find that if you choose mis-tinted paint occasionally (paint that was tinted for someone else sold for much less) for working on accents in special areas of rooms and are discriminating in what you choose, you will save lots of money and find someone else's mis-tinted color is your special color.
This is a page about buying mistake ("oops") paint. One way to save money on paint, if you are flexible on the color, it to buy the paint mistakes at your local home improvement store.