When it comes to NFL contracts the general rule of thumb is that the price is always on the rise. If you look at the quarterback, wide receiver or edge rusher markets (places where the Cowboys could be spending before next season kicks off) the next man up generally comes in at a little bit of a higher rate than the last to put pen to paper.
A position that has found itself trending in the opposite direction for a decade or so now is running back. As time has gone on more and more teams are becoming hip to the idea you do not need to invest premium resources into the position.