With scopes, it can be a bit tricky because there are not any easy and clear cut measurements of quality. The biggest thing you will be paying for is quality of the lenses and their coatings. Because MOST scopes are built from just a few manufacturers, (and in turn rebranded) the level of optical quality is a direct relation to the price of the scope. i.e. you generally get what you pay for. Buy the best you can afford. One think you can look for is light transmission, but that measurement is not cut and dry either. Also, better optical lenses and coatings more then makes up for bigger objective lenses. a 50mm Objective will not make up for poor lenses and is used as a selling gimic. Just pay for good glass, and you'll be happier.
Hope I didn't talk in a circle....
MEL
Hope I didn't talk in a circle....
MEL