An ASM g-3 for $80 dollars is a great deal, but will require a good sized sump, that is the way to go IMO.
If you decide to go with a hang on, the prizm pro deluxe I used to have and sold away is available. That skimmer has been discontinued but did a fair job on my 120 prior to putting a good skimmer in the sump. If interested let me know and I will give you the guys phone number, he switched to fresh water.