Okay, I pretty much agree with what everybody has already said. Get a trainer or rollers instead of a dedicated exercise bike. Also, I am in the camp where riding a trainer was painful to get through, as time seemed to just drag on while I was riding. Do what ever you can to keep it interesting. Ride watching TV or videos and set conditions so you do sprints at certain times like commercials. I heard of some people that ride the rollers during sporting events and sprint during commercials and other changes of speed during live action verses a dead ball. But all of this is to help make it more interesting.
But regarding your question concerning an exercise bike, I still vote for a trainer (fluid if you can) or rollers.