I think just about any skimmer would work on a 10 gallon. The Bak Pak is a great skimmer. I have one on a 40 gallon. With the ease of nutrient transport via water changes, I consider anything less than 10 gallons to not really need a skimmer. If you want to keep some more demanding corals, though, it will definitely help. You can save yourself a lot of money by a) building your own, which is very simple (our DIY section can help you) or b) buy a used one in the for sale/trade forums. A "used" skimmer is equal to a new one, except for the older pump.
FWIW, I built a skimmer for a 10 gallon a while back that cost me $11. This didn't include an air pump and airstone I had lying around, it was just the PVC piping.