All my food is expensive, $30+ per bag, so everything else seems like a bargain to me. 
I do not leave feed out at night so as to not tempt rodents.
Scratch is a treat and not adequate substitute for feed.
How much feed are you going through a week, or a month? I refill a 7 lb feeder about once every 5-6 days, plus a little more (9-10 lbs) in fermented feed, and buy 2 bags of feed about every 6 weeks. That’s for 11 birds.