Perkins can be had for cheap because he's a QB3. But he knows the offense and has developed real nice in his reads. Which is more than I can say about Lock. Shurmur runs the WCO so Perkins wouldn't require much time to learn their nuances. Deal the Rams a late round pick for him, cut Lock, and now you have a depth QB who has been coached up by McVay and company who might help you out when Bridgewater inevitably struggles.
Perkins isn't gonna light it up or anything like that btw. Not saying that. But he can run that offense. Move the chains. And maybe keep growing and if so Denver gets a guy who may be a starter someday on the cheap.