When your scouting report says they "would be extremely interested" it doesn't necessarily mean they are actively trying to leave their current club. Even if they do become unsettled, it also doesn't always mean they will be let go for any cheaper.
First build up your relationship by praising them in the media. Don't praise them too often or the response will be "bored of GrandOurSaviour's constant comments". I'm pretty sure you can praise them mostly every week or so if you choose from the different sets of praise each time, but I usually only do it once a month, starting from the lowest praise first. If the player thinks you have a decent club (at least "would have some interest") you should become his favoured personnel after only a few months of this. This will basically just make him even more interested in joining.
The second thing you need to do is something a bit more forceful to get them interested in actually leaving their current club. You could try a slightly lowball offer and reject any negotiation, but it won't always work. As you know, rejecting other team's bids often really ****** off your own players but, of course, doesn't work nearly as well on AI teams. Declare your interest via media comment and try it anyways, sometimes it will work. Another good trick is to sign a friend of your target from his team. For example, Miguel Veloso doesn't like that Yannick Djalo is transfer listed because they are friends, so if you sign Djalo after building your relationship with and declaring interest in Veloso, his personal happiness turns to "wants to leave the club".
People talk a lot about unsettling players but in my experience it just isn't something you can do for any target you want. If you want to pay reasonable transfer fees, you need to look for reasonable targets based on things other than he is your favourite player. Players who are seeking a move to a bigger club (Akinfeev, Gourcuff, Rene Adler), players who are unhappy at losing friends (for example "upset that the club sold their star player" or "thinks the club should retain the services of player A")... or mad at their manager "feels he was treated unfairly" "feels his manager doesn't appreciate" etc, the list goes on and I'm sure you get the idea. Another great source is teams who have been relegated or teams who are performing below expectations.
People have stories about getting Rooney and C Ronaldo to request a transfer and I've seen them posted here before (probably either FMRTE or fluke occurence of Real Madrid finishing 12th and players losing confidence in manager), but in my experience you can't just snap your fingers at any player and expect him to ask for a transfer. Hope this wasn't too long and that it helps a bit.
