I have no idea why you would need to buy tubing to make a protein skimmer function. It sounds like they are trying to sell you an air driven model? Lets move on and talk about protein skimmers that are available in this decade, as opposed to those dust collecting models on the shelf at your LFS.
First, you have to set a budget. We can spend between $100 and $1000 on a skimmer, and the more you pay the better it will be. I really like the Berlin X2 venturi model skimmer, which you can get for right under $200 from Aquarium Supplies, Pet Supplies and Pond Supplies by That Fish Place - That Pet Place
. It can be used as a hang on or sump model, and is well suited for aquariums up to 125 gallons if used in a sump application.
If your budget is larger and you are already planning or using a sump, then I would suggest looking at the ASM model skimmes. I use an ASM G3 on my 180 FOWLR.