I would go:
Mariota ($1) - former 1st rounder that could use a change of scenery.  Major upgrade over Mannion and could be a starting option if Cousin's contract demands are too high.
Perriman ($1) - Speedy, deep threat that the Vikings had some interest in going back to his draft.  Use him in the slot to keep teams from shading coverage towards Diggs and Thielen.
Jones ($4) and Reader ($2) - Now we fix the trenches...  Jones gives us that disruptive interior guy that we have been looking for and Reader is a tough NT with some pass rush ability.  Let him take over for Linval and Jones lets us kick Shamar over to backup NT where he probably plays best.
Waynes ($2) - He's not a CB1, but he's a good CB2 that has familiarity with the scheme.  He wouldn't be my first choice, but with only $2 left it's a good value.