My initial thought is Britt, Cook, Saffold.
That $13M could be used to help bring back some D FAs. With Johnson, JJ, Barron, McLeod, Hayes and Fairley the Rams have a ton of big contributors on D that are coming up.
Chris Long is certainly a contender as well given his big cap number/savings. I think the team will try to re do his deal. It would be interesting to see how stubborn he may be with that. It is not like he will sign for what he is making in St. Louis somewhere else....not one is going to offer him $14M a year. He is a very good D end but has been riddled with injuries the last two years and is getting older. C Long has been a grinder, hustling and playing with class for many losing teams, I would like him to be apart of it when the Rams turn it around, but, he probably has to help out to have that happen. If he can free up, say, $6M with a new deal/restructure Britt, Cook, Saffold, Long are freeing up $19M in addition to what the Rams already have.
One thing for sure, the Rams have to be aggressive with JJ and Tru. Losing both would be a major blow and there are teams with a lot of money that will come hard after them if they hit the open market. Johnson has been playing well and is a 6' 2" physical corner who plays the run well. JJ is a playmaker.
To me, resigning Johnson, JJ and Barron are the top priorities. Followed by Fairley and Barnes.
Fairley is unlikely as I think he will get pretty big money to start somewhere.