First: What gems are rare and expensive in AH (if you are short of money)?

Second: I need it myself. Take the soldier as an example. I can exchange red for 40 strength, orange for 20 strength, 20 crit and purple for 20 strength, which is what I need anyway. Someone asked me why I didn't exchange two epic gem drawings. I didn't have so many gem coins to do this in the early stage, but I can consider starting with a 67-strength one. )