Actually Graphic Designers don't know need to know much about web development to do their job in designing graphics, images. Of course, if they know some web development it helps a little bit. That is why communication is essential.
As for the hiring trend, it depends what you want and how much you can afford. There is no clear cut answer for that. Prices ranges from hundreds of dollars to tens of thousands. That is why you shop around and ask them questions to make sure they know their stuff.
