Your concerns are valid. You will no doubt be getting a very low quality door at that price. 5200 is actually a very good price for that configuration.
I would look into HMI doors or Provia. Both are made extremely well; very solid and air tight.
Stay away from flimsy Home Depot or lowes doors such as Stanley, reliabilit, Jeldwin, thermal tru.

On quality, an entry door plus two sidelites AND a transom is going to be VERY pricey. I don't know what you could get for $2700, but I would be very concerned as well. The service followup is certainly something to think about also, and likely to be non-existent if the company does not have a local location or some sort of provision to handle it.
HMI and ProVia are top choices, and Polaris and HomeGuard are pretty solid as well. Thermatru is decent, but their products are finished by third parties, so that part can be hit or miss.

Be prepared for the motor freight bill also.

Most motor freight does NOT arrive with a lift gate (though some offer it for more $$).

Just a tractor trailer rig shows up.

It is up to you to get the load off the truck, and it is about 4 feet high and packaged in some type of crate.

If there is a truck depot ear you, you can often have it shipped there.
They at least will have equipment (like a fork lift) and often help you load the crate into your truck.

Even a phone call to schedule drop off costs extra.