Does it have to be pine shavings? I figure if you live near a sawmill that handles many types of wood you could get the shavings from them for cheaper or free if it is ok to use multable types of shavings. I also think if you have hardwoods mixed with pine shavings it would make a better quality compost. From what I seen soil tends to be of poor quality and highly acidic around pines, while the opposite holds true for hardwoods. By mixing the two plus adding ash ect it seems like the compost would be even better for gardening. Perhaps if you have multable coops do half with just pine and ash and the other half mixed pine, hardwoods, and ash. dump them in seperate piles the pine pile being for acid loving plants and the hardwoods on being for "sweet" soil loving plants.
Granted I am very new to chicken raising, but this is my thought process from what I know. If it is wrong or harmful please let me know.