http://overthecap.com/position/4-3-defensive-tackle/
Right now, the elite DTs - Suh, McCoy, Dareus, and Atkins get anywhere from 90 million to 100 million (Atkins got his contract 3 years ago, if he was to get his contract today, he'd be between Suh and McCoy)
Crawford has a total value of 45 million. So he is on par with Linval Joseph and Damon Harrison, which I think is perfectly fine. Harrison averages less than a sack every year, Linval Joseph averages 3-4 sacks a year.
This hasn't even taken into account that players like Aaron Donald and Kawann Short have yet to get their second contracts. I mean, DTs who average 0-1 sacks a year in a 4-3 are getting a contract value of 25 million, Tyson Jackson and Dan Williams.
I have no issue and never had an issue with Crawford's contract. He's a good DT, not great, a good DT that will get you 3-5 sacks a season.