According to John Obi Mikel's agent, John Shittu, Inter Milan have made contact with the Chelsea midfielder in view of signing him this summer:
What I can tell you is that I met with my client and the directors and they are interested in him. He is a great player who has won the Champions League and the Africa Cup of Nations, so he is suited to Inter’s standards.
Inter is a possibility but right now Mikel is a Chelsea player. I cannot tell you anything more on the negotiations. The fact remains that Mikel now has a contract with the Blues.
-Source: London Evening Standard.
Before we get any further it's worth noting that fabricated quotes purporting to be from Mikel's agent are not exactly unheard of, and while I wouldn't dream of accusing the London Evening Standard of doing such a thing, I don't know where they're sourcing this from and am therefore approaching it with more skepticism than usual.
That caveat aside, this deal makes sense for a variety of reasons. Mikel's been phased out by more dynamic players in the last few years, and although he can obviously still do a job in central midfield (see, for example, the 2-0 win at Anfield, or, even better, 1-1 at the Allianz) he's almost certainly never going to be first-choice for Chelsea again. Given his tactical acumen, Serie A makes sense, his ability to hold onto the ball under pressure will almost certainly help Inter Milan out should this go ahead.
How much is he worth? Well, that's down to the clubs, but I wouldn't expect a huge amount of money. High seven figures / low eight sounds about right, and the Standard report that Chelsea will want at least £10 million for him. Sounds about right to me.