Welcome to (posting on) FlyerTalk SnowDogDad ^

It looks like the cheaper fares on that particular route do have some restrictions -- 21 or 14 or 7 day advance purchase (there are progressively more expensive fares at each break), and also some restrictions on days and/or minimum stays.

The cheapest fare (WE21SFN) looks like one that comes out at $311.40 all in if you meet the criteria (Sat. night stay and 21 day advance).