Don't know about cheap, but I can assure you they work very well. A couple of years ago I was coming out of San Antonio heading into hill country VERY early in the morning. All at once I saw something very bright at the passenger side in my rear camera. I pulled over and ran back to check. I found flames 3' high inside and outside the rear cap coming from the tail pipe area. A quick run to the front and the extinguisher and back to the back. I gave it a few good squirts and the flames died way back. After I opened the engine access I found a rag I kept back there for checking oil and other fluids had dropped to the tail pipe and ignited. A check of the area found that the paint was not even scorched. I got the extinguisher recharged at the next stop. Needless to say, I don't store rags back there any more.
Just remember to check the extinguisher monthly and invert and agitate the powder at least monthly. These things work and work well as long as you take care of them. What they look like doesn't count.
