I buy all my filters for the year all at once from Filter1.com. They only sell Wix filters which seem good to me. They have really good prices as compared to any place around here.
Not sure about other peoples usage, but if you’re buying over $500 a year in Wix filters they have a discount program you can sign up for, spring sale also applies as well. A few weeks back I restocked the shelves in the shop, had 2 1/2 of those plastic boxes they ship parts in. I have a spreadsheet I print out for filters, filter number, number in stock, number needed last column is to order, fill it out and drop it off at our parts store and they get em ordered.