I agree with many of the above digressions against the class/career & rank/level system. I would prefer the WFRP career selections, and to those who say that all characters of the same career in WFRP are identical, Ill explain a fix for that later in this post.
As for how to set the fee for "any and all" skill purchases as a elite advance, I find basing the fee off the corresponding Characteristic improvement cost fits nicely. If the skill you want to add applies to a characteristic that starts at 100XP for a simple advance, then to have the skill costs 100XP. 250XP for +10 and 500XP for +20.
Of course, based on the lopsided nature of the prices for characteristic increasements and the honest truth that a skill only gives you access to your full characteristic for that single area of study, a point break may be required.
And additional price costs can be attributed for Basic or Advance skills.
While I do disagree with the overall career approach, I do believe that when you are taught a certain way, certain skills and abilities are more natural then others.
As for WFRP careers, the simplest way to fix the "everyman the same from same career" is to not require all the advances be purchased, but only a certain number, before career swapping. And to use the % chance of having a skill from 1E. Some Rat Catchers have the skill, some dont.