The Telegraph and others are reporting that Arsenal and Arsene Wenger, once acquiring the taste for German international players, are addicted, and plan to extensively scout players like Borussia Dortmund's Marco Reus and Ilkay Gundogan, and Bayer Leverkusen's Lars Bender. All three would be varying levels of "incredibly expensive"; Jeremy Wilson says in the piece that the Arsenal bid rejected this summer for Bender was £18.5 million, and he quotes the other two as "cost[ing] around £20 million."
There are rumors that Reus has a release clause in his contract that would come into effect in 2014 - €30 million, or about £25 million. But not from the most reliable sources - Goal, and Twitter.
Marco Reus. €30m release clause. 27 goals last year. German contingent, German speaking manager.. And Rosicky is his idol.— DC (@DLDN22) September 5, 2013
Bild is a little better, and it appears they say the clause is €35 million, and expires in 2015, but my German skills do not exist and the translation is a bit odd, so honestly it may be saying that the clause doesn't come into effect until 2015. But it appears there is a consensus: there's some kind of clause there, and it's somewhere between £25 million and £30 million. If that's not the case, though, I'd bet he would go for something closer to £35 million, because he's super good.
Gundogan is in a different position. His contract will end after next season, meaning he could potentially be on the move in the coming summer. But while it doesn't appear anything has come of it yet, Gundogan spent the summer in talks with Dortmund over a new deal that would extend him past that, and he's said that he enjoys playing at Dortmund and is open to staying. If they fail to do so, it appears Arsenal would be on the case, but otherwise it's hard to see Gundogan moving for anything close to the claimed £20 million.
Bender, on the other hand, would likely easier to bring in. His current deal ends in 2017, and Leverkusen are a Champions League team this year, but after selling André Schürrle and Dani Carvajal this past window, they may be in for a fall this year. Additionally Leverkusen bought Emre Can from Bayern Munich early last month, who is a potential Bender replacement. They certainly won't have pressure to sell, but at a fair price, it's certainly a possibility.
Scouting players is a very early stage in the process, but when the players involved are of the level of quality these are, it says something of the interest level Arsenal have. You're not scouting Marco Reus to see if he's any good - you know that already. The scouting is more to determine how good, and how the player would fit in. That doesn't mean that the players will come, for sure, nor even that a bid is guaranteed. But one way or the other, it looks like Arsenal have turned their eyes to Germany, and its top-level products. Agents Mertesacker and Podolski may have some more recruiting to do.