Expensive or not? It's hard to say. I'll be anxious to see the terms of the deal the Broncos signed with DT Justin Bannan, though that's a five-year contract for a 31-year-old slated to be a NT in a 3-4 defense. Not a straight comparison.
Robbins will be playing in a rotation, so it's entirely possible the Rams can get some use out of him for a season or two. At 33, it's entirely possible that he will not be with the Rams for the third year of his contract., thus the "as much as" descriptor in the contract news.