How big is your dog? My little fluffy co-exists just fine with our girls.
I think that $25 is reasonable but you could check your local battery farm and rescue some older girls.
How many eggs is variable - in moult they lay none, in winter they lay less and in spring they might lay one a day.
Upkeep is cheap, straw for thier box, table scraps and layer pellets is pretty much all they need.