Actually, I don't think any offer Chelsea or any other team makes could not be matched by Levy. Poch currently makes £2m/year and Mourinho was making £8.5m. I think Levy could easily cover the difference, if push came to shove, and then the deciding factors would be everything else that people mentioned (great academy, chairman support, new stadium, etc. etc.). And that's if Poch was motivated solely by money. As opposed to players, who have just a short 5-10 year window to earn as much as they can to last them a lifetime, Poch is still only 43 and can coach well into his late sixties or early seventies. So motivation to earn as much as he can now, is probably less.
My gut feeling is that Poch wants to build a brand of football, kind of like Barca has done, at one club. And Spurs is the ideal club right now for all the reasons that have been mentioned on this board. I can't see any other of the rich clubs being able to offer that, with the exception of perhaps enticing him with a higher salary. But as I said above, I would see it very difficult for anyone to offer something that Levy couldn't match. It's one thing selling a player, because you will always find new stars. When it comes to coaches, they are so rare that you would be willing to go overboard to keep them and I do believe Levy recognizes this with Poch and will act accordingly should the need arise.