If your name is on the title for that car then your obligated to pay for it. If you don't want it or you aren't going to drive it, see if you can get your name off the title. Whose name is on the loan for the car? If you are on the loan you pay it.
So you talked to a lawyer on the phone and that's it? Did you talk to any other lawyers - you know get a second opinion? I'd be leery of doing it out of court. Did you hire this lawyer? If you don't like what he says get a new lawyer.
Is she still willing to settle on $430 a month?
Lots of people have other bills on top of child support...