Luckily, designers understand this so we get sheer cardigans, which kinda defeat the purpose of a cardigan. However, they still look good without baking you. Fasshonaburu.com posted this one with beautiful dolman sleeves from Tobi. Even on sale, it's $51.
If you're like me and always looking for something a little bit more economical, try YesStyle.com. They currently have a wide selection of sheer cardigans for under $20. Even with the $10 shipping fee, it still puts you under Tobi's price. And it's not $10/item, it's $10 shipping for any order under $150 so you can find a cute summer dress to go with the cardigan and still spend $51.
I love the fashion at YesStyle but my biggest problem is sizing. Please note that "One Size Fits All" actually means "One Size Fits US Size S/M". Girls in Japan and Korea are smaller than the US - call it genetics, call it diet - but overseas distributors don't really cater to the bigger crowd.
Taking all this into consideration, the dolman cardigan is looking like a better investment as far as wardrobe goes. The Ebay selection does offer, however, a zebra print sheer cardigan that would look right at home in my closet lol.