Here is a list of the teams cap space for 2018.
Well. The Vikings are not outspending the Browns. Unless like you say Cousins does not want to go to the Browns, eliminating that option.
The Jets have $72 million. Are they interested?
The Vikings have $50 million. So there are only 7 teams with more cap space than the Vikings right now. One of those 7 teams is Washington who clearly does not want him. Would rather pay Alex Smith I guess (how much was that again?).
49ers will sign Garrapalo. Colts have Luck. Texans and Bucs have young franchise QBs. So the Browns and Jets can outspend the Vikings.
The Cardinals have almost $9 million cap space. They would need to cut some people. The Broncos have $26 million, so about half of what the Vikings have in space right now.
Tough decisions and cuts can be made though which would change this.