It starts from the top on down. Usually once the first pick is signed, it sets a guideline for the 2nd, then the 3rd, and so on. The 1st pick usually gets about 10% higher than the 1st overall pick the year before, though it does get tricky if it's a QB, which is the case this year. Also, Jake Long took less money than the 10% annual raise, so that is something the adds into Stafford's argument as well.
Once the top picks sign, it usually creates a domino effect. But if they haven't, teams such as the Bills are put in a tough spot because there really are no guidelines to go by, and neither side wants to risk getting owned (by signing, then once the other picks sign and the market is set, you realize you could have gotten a lot more).