For a 55g with a sump I'd buy a Euroreef RS80. A second good option for sump would be to get the largest ASM you can find for your price. They are Euroreef clones and you might end up with one rated for a 200g tank that you can use if you ever upgrade. For a hang on tank, I'd buy a Deltec ME300, which is right at your limit for price. Less quality options would be the Coralife 220 Super skimmer. Don't buy the 125 or 64, reports are coming int hat the pumps are not as good and fail early.
For the money you are willing to spend I'd avoid the AquaC. I recommend them to nano guys with tanks of about 24g or less.