Mike, this isn't a dollars/numbers issue.
Someone else mentioned insurance, I'm not sure any company would cover soloing a student in your plane - not to mention giving instruction in it.
And why rent a plane? I bet you've got people with slower aircraft who'd love to swap time in your bird for time in theirs.
Also, why not have your wife at least get through solo in a glider? It's simpler, cheaper, and develops better stick skills.
One pooched landing - a common enough event in primary training - and your theory that using your plane is cheaper is disproven...leaving aside additional wear and maintenance items from primary v. typical use.
I taught my daughter to drive and am teaching her to fly...but I wouldn't teach my wife...
Finally, educate yourself by reviewing current standards for the commercial and also the CFI. It's not one test, it'll be at least three writtens and two checkrides. You can study for and take a ground instructor rating immediately, which can get you a lot of the learning done for very little money...if you put the time in.
I found teaching something a fantastic way to learn it, and I learn something every time I fly. I've also tried to learn something from everyone I fly with.
I also learned a lot about instructing by doing it for a while before trying to take someone from zero to PPL.