what features do I give up if I buy the mechanical disc brake caliper costing one fourth that of another manufacturer?
It depends a lot which specific brakes you are comparing.
If you are looking at $100+ brakes they are probably hydraulic. The high-end market for cable disc brakes is limited because hydraulic seems to be taking over. You can still find boutique brakes like Paul brakes, and there is the Hy/Rd brakes from TRP which cost slightly more. The question of whether to use hydraulic brakes is a discussion unto itself. Hydraulic is favored for low lever effort and not having to be adjusted under heavy use. However hydraulic is also more expensive and has disadvantages of more complicated setup and requiring more special tools and parts.
Within cable disc brakes, the biggest disadvantage of very cheap (generic) cable disc calipers is that sometimes they don't work well, and you may have a hard time finding pads that fit once your current pads wear out. I'm talking about truly generic calipers here, meaning they came with a bike, or they are $10-20. The low end offerings from Shimano and Tektro are in the $40 range, and they work fine. Then again some types of cheap calipers use common (i.e. Shimano) pads, so it really depends on your specific brakes.
Anecdotally, I bought a cargo bike with unbranded mechanical disc brakes. The brakes required too much lever effort for my taste, so trying to improve them, I first replaced the cables with compressionless cables. Then I upgraded to oversized rotors. The brakes were better, but then I installed Shimano cable disc calipers, BR-M375. The brakes became immediately much better and I am very happy with them several hundred miles later.
I bought a different bike with Tektro mechanical discs and the brakes are great. I would say equal to the Shimano. Neither the Tektro nor Shimano calipers are very expensive..$40-50 each. For $60 each you can get TRP Spyre or Spyke brakes which have some nice features but won't really work better than the $40 Shimano.