Buying a scope is a very personal item- many things to consider. What are you using it for... What kind of performance do you want... etc...etc...
I think one of the best resources of info on choosing and purchasing a scope that I've found so far is a book called "The Ultimate Sniper" by Maj. John Plaster--- sounds like a hard-core title I know, and yes the book itself can be up to 40$ depending on where you can find it for sale on the web- but I'll tell ya this book takes it from square 1 when it comes to scopes and by the time you've worked through all of the info with the scope you've chosen you should have not only a well chosen scope but actually know how to use it, completely-- in reality who else but these guys really needs to know their scope?