You can see their fee schedule at: http://www.ryanair.com/en/fees/ — yes, they charge a fee to even assign you a seat.
(Anecdote: I had a printed boarding pass all crumpled up at the bottom of my bag (they let you check in weeks before your flight, so it had to survive for a while) and my poorly kept pass was basically unreadable by their scanners. The baggage check rep printed a new boarding pass for free (without even asking, since she couldn't exactly scan my home printed and crumpled paper)).
Everyone does that now. Delta, BA, AA, Virgin, etc. I can think of very few airlines that give you free seat selection before check-in.
I don't agree with it, but it is the way things have gone for all airlines. Just like baggage fees on local flights (even though that causes mass delays during boarding since now everyone is trying to show too much into cramp overhead lockers).