Your question is whether or not the $30 one is any better or worst than the $100 ones, correct? Correct!
Well, if you read up on ceramic technology, you find that some irons(the cheaper ones) contain plates that are coated with ceramic material and other are solid ceramic plated and this can be the biggest difference. However, many ladies have wonderful success with the $30 conair ceramic technology type irons you get from walmart of target. However, your smoothest shiniest salon-like flat-iron experience will be from one of the expensives ones that contain solid ceramic plates which distributes the heat evenly.
The choice is simply up to you. You can go between and get the generic Sally's CHI for about $50
Hth
~op~