I referenced the P67 because boards between the two makers tend to be similarly priced with AMD boards being somewhat less in price. Since the 990x isn't out, I'm giving my best estimate. As it stands, the highest price 890FX is only $230 on Newegg compared to $340 for a P67.
I still don't think nVidia chipsets are all that much different than the AMD ones now. If you look at the reviews on Newegg, it's not like nVidia boards are any worse reviewed. If you look at the best ASUS boards, the nVidia based one has more 5 egg reviews.