Southampton will not sell Forster. Even if by some miracle they would deal at £30m this late in the window I just do not see that he is better than Hart. Last season he was injured, went on a worldie run when he came back in, then conceded a goal and then went on a run of chucking them in. Basically, he is, like most keepers a streaky, confidence player. He'd just about sneak into my top 10 in the PL list, but barely.
Having said that I'm not a big Joe Hart fan. He has been over-rated for a long-time but he has the experience of dealing with the pressure of winning leagues, playing in the CL and has shown he can handle it. I'd definitely take a chance on an angry, motivated Hart at the right price. The last part is the key.