Interesting point. However, you're not taking into account that that the whole $75 isn't going into Lou's pocket. There's still shop costs (power, heat, water, etc) plus insurance, licensing, costs of minor materials that may not be on the fial bill (tape, welding rod) Equpment costs (tools ain't free), TAXES, plus any number of other tings I could list. Plus, he's still got to make a profit to stay in business.
Now I work in a regualr repair shop (primarily alignment/front end/brakes, plus tires and batteries), we charge depending on the job, but most prices are based on a $70/hr rate. Front end work and brake work is flat rate, but stuff like tires, batteries, and oil changes are a set price, regardless of vehicle While it is a different business, really more akin to a sheet metal fabrication shep, it still works the same way. On the fab shop thing, my dad is a retires Union sheet metal worker, and beleive me, they charged by the hour, not off a set price! And if it took more htan the estimated time to finish the job, the extra cost was added.
BTW, I think you meant "ASE Certified",, not "ACE". I know all about that, 'cuz I'm an ASE Certified Master Mechanic myself.