I would say the majority of people whose wardrobe consists of ONLY preppy clothing tend to have mostly high-end brands since they usually come from a background that can afford that lifestyle. I tend to dress preppy maybe once or twice a week, so I get alot of my clothing from H&M and Uniqlo. I don’t worry too much about brand names when I wear this style since many items don’t even have a visible logo. There are a few items that I own that people seem to only buy for the brand name (Sperry boat shoes, North Face/Patagonia fleece jackets, Ralph Lauren/Lacoste polos, Ray-Ban sunglasses, etc.)
If you really must have brand name clothing but don’t want to pay retail, you have to be a smart shopper and search for clothing at off-price retailers like TJ maxx or even thrift stores