how would something like this be: http://www.guitarcenter.com/Behringer-UB1222FX---B215D-PA-Package-485753-i1527132.gc
Is behringer really that bad? There aren't too many full PA packages that have powered speakers, most of the packages just have powered mixers.
Those PA packages are generally just someone throwing some stuff together. You want to choose a mixer that has the features you need and the powered speakers that will do the job you want them to do.
The fact you said you may have the full band in the future means you're looking for a PA that can handle a full band. With your budget that's just not going to be possible. You can get powered speakers to use as mains now and monitors later so no extra money there, but you'll want a mixer capable of accepting all the inputs you're going to want and that's going to eat your $500 right there, and that's if you skimp on new or find a very good deal on something appropriate that's used.