If you want to discourage players from focusing on talents then don't encourage them to take them by making them cheaper than skills.
10x rank is a VERY high cost. 20 Exp just to get to rank 2 is basically insanity. The players should be able to do something once every couple sessions not once every 4-5 just to reach rank 2 in a skill. or 20 sessions to go from 4-5.
I don't know, with a maximum skill rank being 5, effectively some legendary achievement in itself, I don't think it should be something that players can achieve in a couple of sessions - maybe a few extraordinary adventures yes, but I think it should be something that they really have to work for to achieve.
As discussed in this thread skills are better overall than talents, as they count for every use of that skill, rather than some talents which only work with certain weapons, certain situations etc, so I think their cost should reflect that. Starting with a level 1 skill, it would cost 20 to get to rank 2, another 30 to get to 3, 40 to get level 4 and another 50 to get to level 5, so a total XP cost of 140 to reach the maximum possible skill level...
Is that too high? considering you could potentially get 10 XP from a 'perfect' session.. And yes, I know that's assuming you spend all your XP on that one skill..
I know you probably only usually get maybe 4-5 XP from a session, but I think that stopping the PCs advancing quickly is easier than having to increase the skills and talents of all of the NPCs in the game to keep them from seeming too weak when the players show up and bitch slap them around.