Avoid the Hang on the Back types, they work but are unsightly and not as efficient.
Considering your budget, which is on the low side for a quality one, I would look for a used one. Skimmers are a valuable piece of equipment.
Use the Marine Depot guide below to help educate yourself on the features and brands out there. Euroreef, ASM, Deltec, H&S are some of the better ones to be on the lookout for. Bigger is better when speaking in terms of skimmers. You can always detune them or run them less.
http://www.marinedepot.com/aquarium_protein_skimmers__index.asp?CartId=
(I notice the link does not show what I wanted you to see, click the link and go back to the "home page", scroll down and click on "protein skimmers" on the left and you will see the chart.)
Set up a filter sock and buy four of them. Rotate them every week and wash them by themselves in a washer with some bleach ONLY and air dry. I soak mine in the tub additionaly to make sure they are rinsed throughly. This will help with your mechanical filtration. It is reuseable and very effective. The water will be much cleaner, you will remove material before it breaks down, and the water will be much clearer.
my setup was seen in this thread and is very simple to set up and maintain.
http://www.reefcentral.com/forums/showthread.php?s=&threadid=1147363
Better yet, use the money to set up the sock, save your money until you can buy a quality skimmer. This method combined with a lower bioload and regular WEEKLY water changes of 10% will work fine.
A skimmer, in reality, just extends the time between water changes by pulling out the junk in the water before it has a chance to break down. With the socks, directly plumbed in to the circuit, you will already be pulling out most of it by changing them out weekly and what makes it through compensated with the WCs. When you get a larger bioload where you are forced to do more and more WCs closer together to keep your params optimimal, then you have reached the point for a skimmer.
In fact, I have done the exact opposite to increase my nutrients by removing the filtersock......but thats a different thread.
