In the NFL, there is pretty much a set $ amount and signing bonus established for mid- to late- first rounders and subsequent picks following. There is usually some back and forth and hold outs that results from either 1. a draft pick falling due to team needs and not his ability - he'll feel he deserves the higher pay, or 2. an agent holding a player out while waiting for a similar player (position and skill) to sign a deal - thus hopefully piggybacking on a better deal.
Typically, most late and middle rounder sign quickly, and the earlier round signees begin falling into place right behind. Any team that is in an advatageous position - ie. competitive and desirable to play for - typically will have their first round draft nearly signed before drafting him. Provided the GM is on the ball.
I'd expect Charlie to have a pretty easy time signing with a Green Bay if taken late in the 1st. They are a class organization, have the money, and that slot in the draft for pay and bonus will be pretty well defined based on current salaries and previous drafts. As well, they will take cues from the other 2 QB contracts if he does goes as the 3rd QB as expected.