$320 is not horribly bad if they are turning the rotors. IMHO, I would not put new pads on rotors without turning them, so you made the right decision. A rotor will always have grooves and ridges worn from the old pads. These need to be gone before the new pads go on.
I have been doing my own brakes for years, up until I bought my Genesis. I may continue to do the brakes on the Genesis too, but that depends on how much Genesis wants to charge and how much time I have when I need to do them.
I would never let a Just Brakes, Meineke, etc. touch my brakes unless I knew exactly what parts they were putting on, and even then I would be nervous. A brake job is mechanically very easy-- I might even rate it easier than an oil change, since I don't have to get under the car. But, if a cheap brake shop uses low cost parts, it can ruin your driver satisfaction with the car.
A good set of high-end (non-racing)
ceramic brake pads will be $80 - $100 per pair. Hyundai charges a small premium for their pads at $111, but that is totally consistent with every other dealer I have seen. Throw in another $50 to turn the rotors, and you are up to $160 in materials. Another $160 for labor is high, but not outlandish. You got then down to $256, so that is on the order of $100 for labor. That is a good value for a dealer brake job.
I would hate to know what kind of garbage pads that a Meineke would have put on your car for their dirt cheap quote. They fail the price reasonableness analysis.