A few things off:
1. A protein skimmer will not work in freshwater. Freshwater doesn't form the thick foam skimate due to its lack of well...salt.
2. Any skimmer that costs only 30 bucks and runs on a 20 dollar power head is junk. Don't purchase it if you have sw tank.
3. Surface agitation should be enough to get rid of biofilm. Really it's only a cosmetic problem. I don't really care about my biofilm...
Are you sure they said protein skimmer and not surface skimmer? There are some surface skimming canister inlets and stand alone units out there.