The 3090 has limited stock and is impossible to get your hands on, the chair doesn't. That said I could have bought both at the same time but I didn't have a need for a new chair until now.
Herman Miller pays for itself over time. I spend many hours a day in a chair so maintaining proper back health is important. I expect that I'll have to use that 12 year warranty at least once later on in its life cycle as well.
I could have gone with a Steelcase but you get what you pay for. The $500 less comes with compromises in ergonomics.
For your neck pain Draylo, I'm not a chiropractor but I can tell you that chair height relative to your resting position as well as softness/firmness of the seat can cause neck strain if it's too far out of alignment.