Reversed image print (white letters on a printed background) is about $0.30 / sign more expensive because we have to use much more ink for such a design.
Please don’t forget that a printable area for lawn bag signs is 1″ smaller than a bag size on all edges around the images, for example: a printable area for 24″x20″ lawn bag signs is 22″x18″ (one inch from each sign side).