I couldn't possibly disagree more with the notion that Brad Butler needs to replaced. Haven't you noticed how much better the O-line has been with him healthy? What have the Bills given up, one sack in the past four games Butler has played? I believe he missed all three divisional games, and the line was a complete train wreck with him out. It's looked much better otherwise.
Dockery and Walker, although too expensive, are effective enough also.
Get a legitimate center, and the line will be consistently good every week.