There are many web designers out there that charge very low prices for their work. The problem with these designers is that they are often inexperienced and they are trying to break into the market by offering their designs for a very low cost. The quality often reflects the price tag and the results leave much to be desired.
A good designer will charge based on their experience and the time they spend learning to be efficient at their job. This is the reason why you should always invest in a designer that charges a reasonable fee if you want the results to be worth the investment.