If you want a budget preppy look, I spotted some pieces from forever 21 that'll look great for summer/fall!! (actually perfect for back to school...but that's kind of depressing to mention...>_<)
*note that the links are too the Canadian forever 21 website --> which unfortunately has much less selection than the U.S. site >_< but you can search for them on the U.S. site*
Lightweight Plaid Shirt -CAD $13.50
PLUS a Varsity Cardigan on top -CAD $27.90