I think some members of the public view web design as over priced because it is not a tangible product their getting. They forget to consider, the many hours its has taken you to learn to techniques and also put into the actual project. Then you also have (for some of us) the cost of education, college and university for example.
maybe if we explain to our clients;
The reason plumbers/electricians are expensive is because they have a skill that not everyone can do.
The reason web designers/ graphic designers are expensive is because they also have a skill that not everyone can do.
As far as price in concerned Web design is the same as these trades, you could get your mate to it but it would probably break as soon as they left with the 50 quid you gave them.
phew! Glad I got that of my chest