Hang on a minute...
Protecting your own hearing aside, there's one really big difference.. a proper headset has a noise cancelling mic that chops out the background racket of the engine etc., so that the people you're talking with can actually hear a word you say; a skype headset will not.
In all honesty, you can get a cheapo headset around the 100 quid mark, and it'll last you for years if you look after it. Compared to the cost of flying, it's miniscule.