I had a thread that explained this. Unfortunately, it disappeared. But basically if you want to make anything decent it will cost you 700$. That is usually enough to make people not want to do it. :P
Well it depends, Do you actually want to submit it or do you just want to test out a free version that doesn't allow you to submit games to get a hand of it?
If you have never used flash, you won't learn anything in 30 days. Takes a long time to become accustomed to flash and to actually do anything decent, and the free version where you cannot use it for commercial use is 400$. And that would defeat the point of making games cause you can't submit it anywhere at all. :3