I very much doubt that Apple makes much money on repairs. (Don't get me wrong: I'm sure they don't lose money on them, either.) A good benchmark is that they make, overall, a 30% profit margin, every quarter, like clockwork. Yes, some things are higher (cough app store) and some are lower (cough mac pro), but it's a good bet that repairs are right in that 30% margin area.
Apple devices are, for better or worse, optimized to be high-performance, light, and reliable, with repairability an afterthought compared to those attributes. Replacing an iPhone battery —properly, with a low risk of damaging the phone —requires expensive tools and training, and then the parts are expensive too. There's no evidence to my eye that Apple is charging unreasonable rates for replacement parts or tooling; I look at this program and say "well it doesn't make sense for me, the parts aren't cheaper enough than having Apple do the repair" but the parts are clearly cheaper than having Apple do the repair.
So! If you're doing repairs on Apple devices, you probably can't simply do the same thing they do, except cheaper. That was a silly idea from the start.
Where you _can_ compete is in location -- maybe the closest Apple store is three hours away. Or you could beat them on turnaround time (you're doing this in-house, Apple is usually sending the machine out to a repair center), and customer service. You can offer things like emergency service and house calls. You can charge for these things. Some people will pay a large premium to have a friendly repair tech come to their house and fix their laptop or phone!
The right-to-repair folk have won this fight. Apple has committed to publishing repair guides (they're just there, on the web, today) and selling replacement parts and tooling. They even rent tooling if you need that. But saying that Apple needs to sell parts at cost, or at a loss(!), is silly.