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A close price: newLauch via eBay offers a similar case for $14.99 with free shipping.
A best bet is the T-Mobile Tech21 Impact Protection Flex Gel Shell for HTC Amaze 4G in Teal or Pink (pictured) for $2.45 before the above discount, $2.20 after. With $2 for shipping, that's the lowest total price we could find by $2. It features access to all ports and buttons.
This item is new; however, it ships in bulk packaging.