You just said in your question that you found a cheap, easy to install unit at Wal-Mart, so I guess it should be easy to install. Actually, if you are at all familiar with tools and have a modicum of mechanical abiltiy and can read and follow instructions you should be able to do this without a contractor. If you have a standard height ceiling in your garage you will need the drop down bracketry that should be included in the kit. Be sure it's all there, as some of the CHEAPER units don't include it or some of it may be missing. Check to be sure everything that should be there is there before starting installation and if possible it wouldn't hurt to have a friend around for holding this and handing you a tool if you're up on the ladder, (which you will need), and are already holding something else up. Measure carefully, and be sure to wire the switch and box correctly. Also lining up the safety eyes is critical to proper operation. You should select a mounting point that's out of the way of items that need to be stored, or used frequently and put away. Acutally a second ladder can come in handy to prop up the motor end of the opener while you're attaching the hanging brackets.
40 + years and maybe 15 garage door openers, plus home repairs and maint. of all kinds.