As a general guide, the best values tend to be at the lowest end of a manufacturers best line of panels/series. Don't discount the value of extra size. While one very often hears buyers complaining that they wish they went bigger, one rarely hears complaints from those that wish they went smaller.
http://myhometheater.homestead.com/viewingdistancecalculator.html
http://myhometheater.homestead.com/viewingdistancecalculator.html