When it comes to replacement parts, you get what you pay for 99.9% of the time. You could buy an iPhone X replacement screen for 150-ish USD and it will probably last more-or-less about a month. If you were to buy a replacement screen here from iFixit for 350+ USD the screen will probably last around 10+ years or so and it also includes a lifetime warranty.
TL;DR: You get what you pay for pretty much 99.9% of the time.
For the repair price it is the same scenario as the part cost, you get what you pay for. You only want to hire reputable people to do the repair because if you were to hire a non-reputable person to do the repair things might be inaccurately done or worse, data loss.