I find corallife superskimmers to be very efficient because of their needle wheel powerheads which shread air into very fine bubbles with 18 blades.  It works great and is very reliable and since you have a 55 gallon tank you can go with the small 65 gallon version of it which is anywhere from $75-150 depends where you buy. eBay is a great place to buy new reef equipment, but just until this site grows