I think the salary increases this offseason took the Rams somewhat by surprise. They thought they could re-sign Watkins for significantly less than the franchise tag cost, I don't think they expected Sulllivan to cost so much to resign, I think they figured filling linebacker spots and NT would be affordable - a little more than it would have cost last year, but same general ballpark. The upshot a chunk of the money that was allocated for Watkins has already been spent just taking care of inflation, with holes still to deal with.
I'm not saying don't sign Suh, btw. Just be aware that there will be real costs in terms of player personnel at some point in the near future.