$100 buy a good used one. All you can get for $100 New is probably a Prizm which I equate to buying a $100 brick. They would probably skim the same. Do you have a sump setup on this tank? If not your best bet would be a used Remora Pro HOB or something.
If you want to save some money, skip the skimmer on a sub 50g tank and do water changes. If you don't want to do the changes, buy a quality skimmer like the ER above. Buying a cheap skimmer won't really help the cause much.