flight from Prague to Frankfurt

We will be landing in Frankfurt July 1, our son will be in Prague and needs to get to Frankfurt to meet up with us on July 2. We have checked the options: train, too long a trip. So our flight options seem to be: Lufthansa, too expensive, Czech Airlines, they have a youth fare for about $190, or Ryan Air. Our son is willing to try Ryan Air for $56 since it's so cheap but we've heard negatives about them and he'd have to spend all day waiting for his flight at 20:20 that eve. We know Ryan Air flies into Frankfurt Hahn, not Frankfurt Main, but does Prague have more than one airport? Any advice?
Thank you.
Kathie