Home Depot sells the spray texture in a can that Mark-Ia mentioned. If I remember correctly, it comes with three different sized tubes to put in the nozzle to get different sized texture patterns. It's a perfect match for the spray texture that most cheap commercial drywall jobs use nowadays. Another thing I remember about it is that it's a one use deal. Even though there's a lot left in the can after texturing a small patch, it won't work after a short time. For cheapness, you'd be better off finding a way to match the texture with drywall mud and a brush, sponge, rag, or whatever. For fast and easy, the texture in a can is hard to beat.