Have you researched what other sign companies are charging?
I guess, (even though I might meet with disagreement on this site,) what your other sign companies charge for this same service may be of interest to you.
If sign company "X" would charge $1000, and sign company "Y" charges "$650", then you may have a shot at getting the job at between $1 and $1001. So my advice would be to seek the market rates, know your company's p&l and b/e, and bid accordingly. We've taken jobs that were "off the tops" profitability wise," and also have taken jobs to keep our employees employed. It comes down to the numbers. But unless you know what your market is charging, than anything else is simply a guess.