Cassel got a 6 year 63 million dollar contract with 27 million and change guaranteed from the Chiefs not long ago.
Good 2nd string qbs (which I presume Cassel is considered by most teams) get 3-4 million a year. Matt Moore got a 2 year 8 million dollar contract only a year ago.
So its not like hes doing anything crazy by leaving Minny. Worst case scenario he makes maybe a million dollars less than he would with the Vikings, but hes already made bank and would be able to go somewhere more ideal to live.
Odds are very very good though that he gets a deal close to if not better than what he got with the Vikings though