my math is mediocre so help me. 3/$84MM is $28MM/yr in cap space. Smith is $17MM, so that's $11MM saved. Are you saying to replace fuller is going to cost something like $3-5 MM over what Fuller was making, so net it is only a $6-8MM saved after you replace Fuller? Isn't it more likely they draft someone to start who will be on a rookie contract, or they sign a #2 cornerback / FA at less money than an elite CB?
Essentially, yes. Fuller would get 5-8 million on the open market. That's not elite CB money. That's good CB money, of which Fuller would qualify. If you want someone with a comparable outlook, it's going to cost you some money. He's in the TJ Carrie/EJ Gaines realm.
If they draft someone, they essentially gave up that draft pick plus their third rounder, to get Alex Smith for three years. If they sign someone via free agency, it's the cost of that player minus about 600k.
Either way, the cap savings are far less than than 11 million. 3rd round picks you expect to be decent starters or quality role players. Guys who fill a role that would cost you 2-4 million a year on the free agency market. Now you're talking about burning a first rounder on a guy to replace the player we just traded away. That's awfully steep to get a guy who is 34 and is coming off a career year playing for a guy who is known to make QBs look far better than they are.