You'll get a lot of different answers on this; people talking about capcitance, etc. My advice is don't go cheap-cheap, but there is no reason to spend big bucks either. 5' is kind of an odd-ball size (3', 6', 10' are far more common), but I wouldn't pay much more than $20-$25 for one. Anything less than $3-$5 per foot and sound quality and/or durability will suffer. Anything more is unreasonable to me. The difference in sound quality will be negligible, and it won't be any more durable. Opinions will vary on this, but there are a lot of people who share my view.
Just stick with a quality brand name in that price range and you'll be fine.