I have flown numerous times over the years with my yorkies. I fly Northwest. I have found that the $$ are forever going up. I flew in Jan for $60. less than I flew in Sept. I can't recal exactly now but I think it was $180. plus your certificate that the vet charges around $40-50.
I just have a little soft carrier that I put in front of me under the seat. They will ask you the dimentions of the carrier.
I have had nothing but good times flying with my dog. They say you can't take them out but I always have put her on my lap, she just sleeps. I have never had anyone say anything except the last time I flew after the flight the stewerdess said that she saw I had her out and I wasn't supposed to do that and not do it the next time! I didn't listen of course, and nothing was said on my return flight. In fact on the way home I didn't even have her in the carrier when I boarded the plane, I had her in the great front pack that I got from Toyville.com. They didn't even know she was in there!! She loves to sleep in it and it has mesh sides she can see out. Most people love our little doggies. Mine have been under 4 lbs so some people don't even notice there is a little one.