It sounds like you have a great plan. Very similar to what I do. If you have a Facebook account, do yourself a favour and join this group https://www.facebook.com/groups/225827837965816/ Lots of useful DIY bear hunting info on there.
It sounds like you're expecting your bait to last 1 week between re-fills, so your barrel design will be important. Once bears find your bait, they can be on it all day and night 24-7. The volley ball sized hole with the logs shoved in it will be cleaned out in no time. For bait, unless you find a connection for something for free, the cheapest way to fill a barrel really does seem to be popcorn. (Unless you put a lot of value on your time spent popping it.) A $35 50lbs bag of kernals will fill nearly 3 barrels. Whole corn is another relatively cheap option to add something that will fill bellies. A local farm here sells 50lbs bags for $8/bag. Each bag is about 6 gallons. So you can do the math for volume required. Less than half the price of the cheapest dog food you'll find. I primarily use popcorn due to the weight, but bears sure can eat it fast if your barrel allows it. I think i could eat 50gallons of popcorn in a couple days myself! :D I've finished popping mine a month or so ago. 6 barrels worth. Start over the winter. When you're doing something in the garage, run the popper. Filing your chainsaw chains, run the popper. Changing oil on the mower,,, Popper! :D
Deer feed (whole corn + molasses) is another option and it's often on clearance sales.