Well, according ot an NFL.com article:
Should Harvin maximize the remaining escalation available, he'll have a base salary of $3,343,750 in 2013 that would bring his earnings (base salary plus workout bonuses) over these next two seasons to $4,313,750. That's still a bargain for the Vikings, who have been reluctant to pay Harvin given their concerns over his ability to remain healthy. If Harvin reports on time and produces at a high level, the team may be inclined to rework his contract next offseason.
The article explains all the contract escalators, but the bottom line is that over the next two seasons, he will cost AT LEAST 4.3 million. He's worth every penny and more.