I wouldn't go for cheap if you were trying to protect your iPhone. There are a bunch of nameless companies selling cases at Walmart, Best Buy, etc that aren't that good for the money.
I'd shell out $20 or so for an on-sale Otterbox though.
It supposedly performs just as well as the Otterbox and weighs much less and costs less. I own one and love it. It just radiates quality and it looks GREAT. You can choose from some great colors too.