All of the hammocks I mentioned have built-in mosquito netting.

It's very true that you can tie a hammock up out of a cheap bit of cloth and some rope, but the commercial ones have enough cool extra features to make them worth the cost, IMHO. Double layers to keep insulation in place, ridgelines to keep hammocks hanging with the correct amount of sag and hold up your bug netting, cut and sewn fabric to give a more optimal shape and more comfortable lay, etc etc etc.

Lots of folks hammock very successfully with nothing but some fabric from wal-mart, but plenty of us appreciate the extra features you get on some commercial models.