Although this thread was resurrected from the dead, those questioning the price of the work need to understand one thing, if you don't ask for it, you won't get it. Perceived value is relative like everything else in life. If the client understands that he will make more money off of your sign than you did making it, it then becomes an easier sell. It's up to you to educate your customers about the value you bring to them.
I just sold a really large job for $30k which is twice the amount my competitors would have charged. I said its would cost x amount and they said great, just so it's done before the end of the year. Ask and you shall receive is a quote I heard somewhere before.