And keep in mind, you'll want to be giving your employees a pay raise as well. They'll know what the clients are paying. Not a 1-to-1 increase, but maybe 30%. Make sure they realize you value their work.
$300 isn't unreasonable, there is a small dev shop in town with a proprietary CMS that charges $315 for creative/development work; and they're one of the most successful around town.