If you are crafting to increase your CP level, don't craft with expensive gems, that's a waste. Make rings that use cheap metals and common stones. I am a tanner and I would be silly to craft 'gloves of the owl' using a ruby each time trying to increase my crafting points. That being said, I understand your frustration. Leathers are more valuable than most of the boots and gloves that I can make so when I have surplus leathers - I sell them and make a great profit. As for the cost of the bars you use - that is a function of the open market and cannot be controlled by the game designers. If there were more bars available on the market, then the price would come down and you would see miners crying on the boards.
I suggest that you increase your crafting experience using cheaper materials, and when you get to the point were you are crafting a lot of rare/legendary/epic items, then start using the valuable gems because then you can really sell those sapphire rings for a great profit.
