We'd have to send out somewhere between $17 million and $18 million in salary to bring Gasol back. That's a lot to come up with.
I believe Lee, Bass, and Green would get it done economically.
Whether or not it's worth it is an entirely different question. I say no, especially because we could get the younger Josh Smith (sorry) for less... Lee, Bass, Sully, and a pick, maybe.
Problem with that idea is Smith is on an expiring deal and as you said, is much younger. There's a much bigger market out there for him, and someone is likely to beat that offer.
Pau however, could probably be had at that price, as there isn't much market out there for him. Question is if it's worth it, does Gasol make you that much better this year than Bass does? The loss of Lee is fairly marginal, since Bradley will be back and Barbosa is there. The loss of Green hurts a bit, as you have no primary back up to Pierce then. You have to bring in a Pietrus, or have truth in Kris Joseph to get the job done.
That's a lot of risk to take for an aging post 30 year old who's clearly in the decline.