I've searched for almond flour a thousand times and honestly, regular supermarkets almost never have it at a good price, but it's worth checking the gluten-free or dietary product sections because sometimes you get lucky! If you don't find anything decent, bulk stores or local health food shops usually sell generic brands that are way cheaper than supermarket ones, even if you have to go in person. Another option is to buy whole almonds and grind them at home with a food processor (it ends up way more economical if you bake often), or if you prefer ordering online, some marketplaces have good deals on large packs that work out cheaper per kilo.