I know you didn't ask this, but another option is $25 at Lowes or Home Depot. You could get a 2x2 piece of plywood, a couple of steel brackets, and some lag bolts to make a shelf. They'll cut the plywood to size for free. If you're like me, you probably have some paint sitting around to spruce it up. If not, both stores sell "sample" sizes of paint for $3 that would cover this project. As long as you screw into 2 studs, you'll have more than enough support.
It's such a small project that it might be fun for you, you could save a few bucks, and have your mount today.