I wouldn't be upset with some type of contract that is mostly bonuses and whatnot especially later in the contract. Don't want a ton of guaranteed money because running backs are so expendable.
And while I admit that Forte is one of the better backs in the league, he's not the best. Giving him a ton of guaranteed money could easily come back and bite the Bears in the ass. As much as Forte refuses to admit it, running backs get injured and he's already suffered from injuries.