That's a pretty dim view of the possibility of JG going to Chicago.
First lets look at Cousins. There is no way that Washington is going to let him go after the kind of season they are having. They will either franchise him again, or pay him what he wants, much like Flacco had the Ravens over a barrel in his FA year. Mark my words, Cousins will never see true FA. Besides I'm not sure he's THAT great a QB, and is more valuable to Washington than to another team.
Tony Romo is another reasonable option, but again, what is going to be the price to trade for him, and is he the answer for a young team that is building a roster. Romo will be interesting to a team that feels they are just a decent QB away from being a contender, not to a team like Chicago.
As JG, he's perfect for them. He's got 3 full NFL years in the most complex passing offense in the league, and has shone on the field he can direct it effectively against good defenses. He's from the area and would be a real plus for their marketing department. Finally this QB class is reportedly not that good. Whatever QB they can get at #3 is likely to be long on potential and not ready to play in the NFL, or at least lead a team to the playoffs and superbowl contention.
Now maybe the #3 pick is too high to give up for a QB with only 2 games of actual playing time, not matter how good that time was. There are a lot of ways to get around that. They can give the Pats their 2nd rounder this year, with a first rounder in 2018 conditional on the Bears extending JG after the 2017 season. So if JG is a bust, the Bears losed the 35th pick in the 2017 draft and maybe a 5th in the 2018. If he's as good as advertized, the Pats will get the 35th pick in the 2017 draft and a first round pick that is likely to be in the middle teens in 2018
That would be fair value to both teams. Drafting QB's regardless of how high they are picked is still a monster crap shoot. Using that pick to mitigate that risk by a LOT is actually smart. JG in the 4th year of his rookie contract is probably a lot cheaper than picking a QB #3 and paying him. Top picks even under rookie contracts "get paid"
BTW- another way to lower the cost would be for the Bears to trade down from the #3 spot to somewhere in the top 1o and THEN trade the pick. That way they get their QB AND add picks in the future and/or lower rounds.