A little advise about skimmers. Don't buy a cheap one, it won't do the job and you will just end up dissappointed and you will buying a different one in a really short period of time. (been there done that)
The reason most cheap skimmers are for sale is because they simply don't work or don't work well. So, the best advise is don't waste your money on one of the single most important devices you need to be successful in this hobby.
If you decide to buy, most experienced reefers agree that AquaC, EuroReef and ASM (and a few others mfg's) make the best, easiest and most consistent performing skimmers.
All that being said, the reason I noticed your post is that I'm selling an ASM G2 skimmer. On my tank (75g/30sump/20fuge) I have it collecting very wet and it will fill the cup every 1.5 days. Or you can collect dry and you cat get very dark nasty skimmate. I'm selling because I am ugrading to a larger ASM skimmer. Which proves the point I was trying to make above. This is my fourth skimmer THIS YEAR. The ASM is the only one of the first three that actually does a good (read: very good) job.
Edit: I sold my skimmer, but my recommendations above still apply...