Can't tell you about sleeping in fire stations or churches; never tried either. But, I can tell you that even the crappiest motels along the southern route will charge you $50 to $60 a night. Going from West to East, your weather should be fine, so long as you stay out of the Rockies. (Not quite sure what you mean by the Southern route as there are several of them.) If you need any info on Southern California, let me know.