Here's an alternative that makes purchasing advances for experience points more simple and elegant.
* Each Advance is +5% (not +1)
* Costs for Characteristics and Skills use the same, vastly simplified, table
* To find the cost of a Characteristics Advance, use your total score (starting value plus advances, rounding down to nearest 5%)
* To find the cost of a Skill Advance, use only your skill
Example: Burgha wants to increase her Initiative, currently at 36%. (She has already purchased one advance; her starting score was 31%) Purchasing an advance at 35% costs 300 XP. Her new Initiative Characteristic becomes 41%.
Example: Burgha then wants to increase her Intuition skill, currently at 61%. Her actual skill advance is 20%, so the cost is 150 XP. Her new Intuition Skill becomes 66%.