The cheapest ones that I've found that are light are the Weyless ones from Supergo. The bolt-on's weigh 16 grams for 31.8 and are about $7 and they have QR's also. JensonUSA has the Hope seatclamps, bolt ons are a claimed 19 g's.
Regardless of what brand you get, QR's will generally be more than twice the weight.
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