Tate isn't going to get big money anywhere, for the reasons you listed. He is at best a #2 receiver in this league and he will be paid accordingly. We should be able to retain Tate and Baldwin relatively cheap, I think.
ET should be the number one priority to resign. He is more important to our defense than Sherman is, and unless Sherm gives us a hometown discount, he is going to be commanding top dollar in the league. It would be great to hold on to Sherman, but I think it's about a 50/50 shot that he stays in Seattle for a legitimately smaller amount of coin than he'll get from other organizations. We can definitely back load his contract and give him a fat signing bonus that will get spread out to help out the cap situation, but I don't know if it is 100% possible with arguably the best corner in the league.
However, I think our defense should be left for a different conversation. Our offense could really use a big talented guy like Davante Adams, Allen Robinson, Jordan Matthews, or Mike Evans. Having a big target that can win the 50/50 balls and take the top off of a defense would be amazing considering the talent we have already with guys that are great in space.