The problem with web development, especially back end, is that the work is not visible. Even with front end the effort that goes into, let’s say a logo for instance, can be hours of work.
I world say that he is probably not ripping you off. The price is actually less then I would get. If you have a trust issue, it is perfectly reasonable to simply ask him what he did. If he is running an honest business, he will happily tell you where your money is going. If he gets nervous and doesn’t have the answers, then maybe your hunch is right.