Also when you have an idea of what skimmer you want, look for some used ones. Far cheaper than buying new. I just recently bought a skimmer from a local guy, $300 with pump. It'd easily handle 400 gals.
I also agree with this, but only to a point.
When you buy used check it out carefully, and make sure of the following -
It comes with all the original parts, or replacement parts are obtainable.
The unit has not been damaged or hacked, or it can easily be put back to it's original state. (I use hacked in this sense meaning that the unit has not been ruined by poor modifications. I am not talking about generally accepted modifications done to make a serious improvement.)
The unit has no major repairs that may cause a failure in the future.
Always check out used equipment very carefully, because one you buy it, it's all your, including the old problems it may have.