Two months ago I used mileage to book a seat in Delta's Comfort class (same as regular cabin seats but more legroom)

I probably got ripped off but it cost me 40,000 miles each way. About a month ago I decided to find out the cost to upgrade to first class. I was told 17,000 miles plus $150 EACH way. No thank you

Two night ago I inquired again. New cost to upgrade to first class: 10,000 miles each way with no dollar charge. Needless to say, I'm going first class. By the way, I just checked the Delta website. First class is 100,000 miles EACH way. Go figure. Why would they only charge 10,000 miles each way?

Bottom line is it might not be that expensive to upgrade to 1st class with miles.