Seems similar to what 82games.com did last year.
Detroit Pistons NBA stats and data from 82games.com
Except, they determined that Billups should earn $24.07 Million. Sheed was at $13.8M. Of course, that was 2005-06, when their numbers were outstanding for the regular season.
My point is tha the numbers can jump around a lot from year to year. If Billups does something close to what he did in 05-06, we will have a great bargain. If he repeats last year's production, then we will have a player who is receiving a fair check. Looks like there is more upside than downside to me... barring injury.