When did movie take place?

Movie initially seems to mirror era in which book on which it was based was published--all clothes, cars, behavior ("innocently" kidnaping an albino, etc. appear to reflect Hollywood-ized version of early Thirties/Great Depression as experienced by bunch of southern hillbillies). But halfway through film, characters drive into town and streets are filled with mid-Fifties cars, Eisenhower era beer signs, etc. Were audiences supposed to believe that these characters were living in huge time warp or just assume that production budget wasn't big enough to redress major locales in period decor? In any event, confusing.