Here's what I've gathered:
the amount xp per level is (kx)^10. For skills, that k value is about 0.01. Each job has a different k value. This essentially means that you need 1024x the xp to double a skill.
Most skills increase your stats linearly, and any skills that don't will instead increase your stats logarithmically. That means to increase the stat by 1, you have to multiply the skill by a certain amount. Each stat has a different base for the log. Bargaining's stat is a divider on prices, but the game only shows you the multiplier.