First question: via HDMI or component? If HDMI, then I would be looking at the Oppo 970HD for $149 and be all done. If component, then I'd go with the Panasonic.
The main difference IMO, is built qualty when you are talking price. Very inexpensive players tend to not live quite as long. Yes, you get better DACs and often better video processing (the Oppos are a bit of an upstart though), better audio and video control (calibration), etc... but it really depends on what you are after. If you just want something that will play movies and you aren't looking for all out best picture quality, then the $99 players should not disappoint.