Cardigan sweaters are such wonderful pieces to own. You can wear them over and over, and people will never question you for wearing a cardigan a couple days in a row, but don't expect the same if you wear a shirt multiple times in a row. That's why I think cardigans can be worth spending a little money on, especially if it's a basic color and classic style, so you can wear it for a long time. I especially love the slouchy cardigans these days...they have stolen my heart. Warm and cozy or light and breezy, cardigans are so diverse and here's some I love: (once again from most to least expensive)
Above, from left to right: Zucca, $652, Helmut Lang, $520, Urban Outfitters, $168.
Above, from left to right: All Saints, 75 Pounds, or about $138, Free People, $108, 7 For All Mankind, $88.
From left to right: Urban Outfitters, $54, Gap, $38, Forever 21, $22.80