At his pre-Chelsea press conference, Arsene Wenger was asked about Edinson Cavani; specifically, Edinson Cavani and the chance that he could join Arsenal this January. The Arsenal manager responded, not with his usual denial, but with a rather more interesting confirmation of interest:
Cavani is a player that I like. Will he cost a lot of money? That's for sure. Nobody would deny that. [But] our banker lives just next to me at the moment and he is ready if we find the right player.
There are a few reasons why this seems unlikely. First of all, Cavani has a release clause of €60m written into the new contract he signed this year, that extends until 2017. Right now, Napoli are third in Serie A, enough to get them to qualify for the playoff round of the Champions League. They're 2 points behind Lazio, who are in second, an automatic qualifying spot, and just 5 points behind Juventus. There's a chance, a small chance, but a chance, that they could win the league; at the very least, they could finish second. On the other hand, they're just 2 points ahead of Inter, in 4th, and an Europa League spot. Selling Cavani, Serie A's top scorer with 16 goals, and a major reason why Napoli are in third, would hurt their Champions League chances.
Secondly, even if Arsenal were to bid £30m for Cavani, and cover the signing fee and wages, they'd likely be out-bid. Chelsea may have signed Demba Ba, but Cavani is a player who has interested them for a long time, and Fernando Torres is kind of rubbish. Manchester City would likely be interested, especially as Mario Balotelli is rumoured to be leaving for AC Milan.
So while the idea of Arsenal spending lots of money for an undoubtedly world-class player like Edinson Cavani, there's really no reason for Napoli to sell now, and they'd probably be outbid anyway. That's how the transfer market works for Arsenal. But maybe they can take that £30m and use it to buy a defensive midfielder, and a creative player. Those are altogether more cheaper.