Having had a few lenses repaired I can offer my own experience.
Best advice, use only an authorized repair center listed on Nikon's site. You can send it directly to Nikon but my bet is they will not quote you anything over the phone and without inspecting the lens either.
I would see which repair center is closest to you. Mine happen to be Sanford Camer Repair in Arlington MA. They have repaired 3 lenses so far (I have two back and one I just dropped off). They do top notch work from my limited experience. They will not quote anything on the phone or in person. They do a complete diagnosis and call you.
Now you might get lucky and have someone that will quote you a CLA (This will be done if they have to take apart the lens) and the cost of the element and labor. There may be more damaged inside that you cannot see or detect.
Bottom line is if you think the lens is worth repairing and you like the lens, send it in for repair. It will be less than the cost of a new lens and anything that needs to be fixed/replaced will be.
Are the scratches affecting the pictures you take or is it just cosmetic and bothering you to see?