For now, I would not recommend paying for Pro accounts until some of the service's problems are solved. Once they are, however, you can purchase three different Pro accounts. Pro I provides 500GB of storage for $10 per month. Pro II includes 2TB of storage for $20 per month, and Pro III offers 4TB storage for $30 per month.
Dotcom and his friends have big plans for Mega. Feature enhancements slated for the coming months include mobile apps for multiple platforms; calendar, word processing, and spreadsheet Web applications; instant messaging; and desktop file mounts for Windows, Mac OS X, and Linux. Let's just hope the team fixes Mega's bugs before adding new stuff.