If Santana is so good, why not just keep him? And as mentioned, he's pretty cheap too. If you're just looking for a defense-first 1B, those guys come cheap and aren't going to cost you Santana.
I don't see a MLB 1B for 1B swap unless you are taking on a bad contract or there are some odd circumstances. We've gone over this a bunch in this thread, but the main types of trades are either 1. MLB player(s) for prospect(s), 2. prospect(s) for MLB player(s), 3. MLB player for MLB player at another position, or rarely 4. prospect for prospect at another position. You don't see teams trading for and from the same position in the same MLB deal.