craftgrrl | Casting resin and coasters

I've been looking around for coaster-making options. I had trouble finding a coat to go over art that wouldn't be tacky/the finish would be off, and glass is much too expensive. I was talking to a girl at my local art supply store and she suggested I try casting resin. Before I go nuts and spend $45 on a tin of material that might not even work that well, I implore you for any advice/experience with coating things with resin. How well does it stand up to condensation? And will make ink bleed on printed papers?
I just want to make coasters for naked coffee tables everywhere! Help!