I'm trying to work within the framework offered in RAW, individual skill costs are not in the cards. Not because I am against it but I'd rather not tweak everything at once. 
Makes sense. I think then that you are good to go with the costs as is.
I can't help myself though, always had a soft spot for arcane users. There might be a "triple" hybrid showing up as well. 0:)
That's why I did give individual costs for the Archmage too (basically, I recreated him using the RMU profession creation rules, with the Sorcerer as the base, then modified him with my optional method for providing individual skill costs to approximate the RM2 Archmage).
