Okay, let's rename the social classes lower, middle, and upper. For now the technology is medieval, with magical influence going back to when specimens of the genus Homo exhibited magical talents. Environment Class gets renamed society Class. And I've added Profession. So...
Class Class: Lower Class, Middle Class, and Upper Class.
Society Class: Savage, Barbarian, and Civilized.
Character Class: Fighter, Cleric, Wizard, and Rogue.
Profession: A whole bunch.
To give you some idea of how skills, and character improvement, work...
Each class has native skills. These are those skills a character learns as part of being a member of that class. Lower Class characters have basic Crafting skills. Trapmaking: Weirs for example. Skills native to another class cost more to learn, and thus take more time. Thus for a Lower Class character learning Etiquette/Social Graces can take up to four times as long depending on factors such as Society Class, Character Class, and Profession.
So a Lower Class/Savage/Cleric would learn Rogue skills at a lower cost than an Upper Class/Civilized/Fighter (Knight) would.
The time it takes to learn the skill depends on how fast the character earns experience, and how much experience each point needed to learn the skill costs.
This is where it gets complex.
For this d20 variant I started with the premise it takes a base 1,000 experience points to earn a level. All levels. Characteristic range I changed to 1-20. The player rolls 2d8 plus a d6 and subtracts 2 from the result. Assign as desired. Each Character Class has one or more governing characteristics. For a Fighter it would be Strength. For a Paladin it would be Strength and Wisdom.
How many experience points it takes to earn a level depends on the Governing Characteristic(s) for the Character Class. The lower the Governing Characteristic is, the more experience it takes. To determine that divide 1,000 by the Governing Characteristic as a fraction of 20. So for a fighter with a Strength of 18, 1,000 experience points would be 18/20th (9/10th) of the actual score needed. (1,053 to earn a level in the case of our Fighter.)
Now we introduce Skill Cost. The points it takes to earn a rank in a skill. The harder a skill is to learn, the more points it costs. Skills also have a governing Characteristic or Characteristics. Yes, a lower Governing Characteristic means it costs more to learn a skill. Spears are relatively easy to learn, so for this post I'll assign a base Skill Cost of 5 to the skill. For our Fighter that 5 points is 9/10th of the true cost (Strength being the Governing Characteristic), or (thanks to rounding) 5 points.
At this point I need to decide on how many Skill Points a character gets everytime he earns a level. You divide the character's real Experience Point cost by the number of Skill Points he gets, then multiply that by how many points it takes to raise a skill. Means more research and more thinking and hard mental stuff like that there.
In case you're wondering, when all's said and done yes, I do get rid of levels. All this talk about levels and experience needed to gain them, and I wind up dumping levels all together. I am evil.

But it is necessary to explain how I arrive at the experience cost for improving skills for individual characters.
Don't know if this helps any, but I thought you'd like to know some of my thinking.