1. There are plenty of online tournaments with prize money, but not here on chess.com that I know of.
2. The participation fee is higher the more rewards that are handed out. It really depends. I've seen some just $30 dollars, others are upwards of $70-100 or more.
3. Each tournament can set up different categories, but often it is U1400, U1800, and Open.
I have never participated in online tournaments so, I have few questions about it:
1. Are there any online tournaments with prize money?
2. if yes how much is the participation fee usually?
3. how are the categories divided? will I be competing within my rating or is it separated by age?