Vintage slips are a must-have for summer--they're sexy and cool and comfortable and there are about a thousand ways to wear them. Let the lace hem peek out from under a sundress; tuck one into a pencil skirt and it becomes a camisole; layer a couple different colors and they become an awesomely slinky summer dress; or just wear one around the house when the air conditioner breaks. We've rounded up a rainbow of options from Etsy sellers across the country, and guess what? They're all 20 bucks or less...