This is another one of those questions that many younger moms have asked me over the years. Here are a few things I've done over the years that have helped me keep our crew shod.
First, I keep the shoe wardrobe simple. In the spring/summer, the girls have sandals, tennis shoes, and white dress shoes. In the winter, it is tennis shoes, black dress shoes, and usually some kind of slip-on casual shoe. This is partly for sanity's sake and partly for budget sake. Yes, I love shoes, and in a perfect world I would love to outfit each girls with boots, and several different colors of shoes. But since I have so many girls, I would have to do it for all of them, and it just isn't feasible. Now that Kora's foot has finally stopped growing, she has more shoes than she used to. This is partly because I saved many of my size nines that didn't fit me anymore for her.
Second, I don't buy my kids used shoes. I do buy used clothes, but not shoes. Right or wrong, my reasoning is that I pass them down to the next child, so I want my kids to get as much use out of them as possible. But that might not work for someone with fewer kids. I have bought the largest majority of their shoes from Payless and Target.
The biggest savings I have found over the years is the Payless BOGO sale - buy one, get one half off. During this time I would go through the store keeping my eye out for sales, especially clearance sales. At the end of a season I would look out for shoes they were clearancing out. At first I would try to guess at what size Kora might be the next fall, if I was looking at black dress shoes, for example. If she was a six right now, and was growing about one size a season, I would buy a size 8 black dress shoe on clearance.
This usually worked. But as I had more and more girls, I would not worry so much about whether it might fit the next year. If Kora grew more than I expected and needed a 9 instead of that 8, I had three more girls waiting in the wings, and they would eventually fit somebody. Tennis shoes were my favorite. Since they are worn year round, if I found them on clearance or a good sale, I would buy them if they were bigger than what Kora was wearing now. I can't tell you how many times I found tennis shoes on clearance for $5 or $7, and with B1G1, I would buy two pair for $8-$11 total. They might not get worn for a year or two, but they were waiting for my girls when they got to that size.
Following these strategies, I rarely have to take the girls to the store to buy new shoes at full price right then. Occasionally it has happened, but usually we go shopping in the closet shelves in my stash. Granted, I was able to do this in large part because I have all girls, and could take advantage of sales that way without worrying over much about sizes.
I have huge Rubbermaid type bins that I keep the outgrown shoes in, and when someone's foot grows, we go shopping in the bin. I do occasionally have to replace the hand-me-down shoes, usually the sandals. But I try to keep a list of what needs to be replaced so I can keep an eye out for them on sale (especially in late summer early fall for the sandals when they go on clearance). I'm not buying as many shoes now since Kora has gone all the way up to a women's size 9, I have shoes waiting in all the sizes underneath that.