I don't understand buying a car that's physically uncomfortable to sit in.
It's one thing if the seat is uncomfortable after a long drive; you'll never get that from a test drive. But this would be bugging me from the minute I sat down, and I'd never buy a car with that issue - no matter how cheap it is, I have enough neck problems without them being exacerbated by my car.
I'm sure you're aware, but that's pretty dangerous. You will most likely have pretty bad a neck injury if you get into a wreck. It might be worth upgrading the seat to one that fits you better.
He'll likely have a pretty bad neck injury without the accident. Keeping your body in an unnatural alignment like that for long periods of time is just begging for spinal injury.