The whole problem with all of these proposed free agent signings is that the discussion will go something like this:
PLAYER: You really want me in Houston? For what, exactly?
LUHNOW: We have a very important job for you. With your talent and ambition on our side, we can go from 105 losses to 95 losses and show the Average Fan that we are Really Trying. It will be epic... OK, not quite epic. But mildly exciting... or at least slightly stimulating. I think we can do that.
PLAYER: ......
LUHNOW: I can't believe you're not more enthusiastic about my offer. You look nervous. Is it that guy behind me? Don't worry, Jim is not nearly as creepy as he looks on TV. Well, not quite as creepy. But he's genuinely loveable once you get to know him, in a completely non-obsessive and un-stalky way. Honest!
PLAYER: You're serious. Really? Well then.... Show me the money, motherfucker!
tl;dr... They're going to have to grossly overpay for anything vaguely resembling a big name free agent.