That $17.00 is retail You can but your last stale 2 day old doughnut that a plumbing co is only paying 1/2 that price if not less if he buys in bulk
Then he is also saving money on man hours.
He saves 15 minutes per valve installed , In a 2 bath house that is 14 valve that is 3 man hours saved per building. if you do 200 buildings a year 600 man hours.
Yeah, yeah, yeah...if you look at everything as "how can I save" you set yourself up for trouble. Do you want to know how much in reality was saved with the [toxic] cheap drywall from China? Looks good from the start... Shall we talk about aluminum wiring? What about polybutylene piping? Yeah all of those "great ideas" were done ONLY for the builder or contractor or repair person, only to save money, and NOT AT ALL for those who have to live with it.
Perhaps I'm in a minority; when I build or repair or otherwise maintain something in my home, I ALWAYS ask the question "what do I when it fails?" and I always assume that I will be the next person working on the project. You learn very quickly that if you do something stupid to save a few bucks, it may very well come back and bite you.
But to each their own. If one likes the neat tidy look of a recessed stop for a toilet valve, well, go for it. I just see trouble waiting to happen with a wall repair--and if you don't have access to another shutoff, you may have to cap that off after you hack a hole in your wall and wait to get the repair parts.
No thank you--not for me!