There isn't enough lessons in leveling alone you have to make gold to turn into credits and make the most of house/city credit sales. Alternatively there are "No Brainer Lessons Packages" you can buy twice which gives 1000 lessons each for IRL money.
You gain lessons in various ways: Leveling, bound credits from leveling (you get a total of 300 bound credits going from 1-100), buying credits in-game with gold from individuals or organisations, participating in special events that may reward credits or items that can be traded-in for credits (like the Wheel of Fortune), and purchases from the website: www.achaea.com/credits
In most cases, the easiest way to get to Tri-Trans (your three class skills transcendent) would be to purchase the No Brainer packages via the website. You can buy two No Brainer lesson packages, giving you 2000 lessons for $20 (two packages of 1000 lessons for $10), and then a third package, 300 credits for $49.99, which is a discount of roughly $60 USD.
After those options, the most fiscal way to obtain credits and lessons would be to do the Iron Elite membership. $24.99 a month gets you 100 credits (increases by 5 credits up to 120) per month, an xp boost, and 5 lessons per RL day (so 5 credits of lessons every six days). You also get a bonus to credit purchases (not the No Brainer) and discounts on certain promotions, like the Artefact Cart.
By far though, the No Brainer lessons are worth it if you plan to play for any extended period. $20, and you will get most of your class skills if you have been leveling at a reasonable rate.
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