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Buy.com has the Microsoft ZJA-00001 Arc Mouse for $34 after $16 instant discount, which is a 31% savings from the $50 list price w/ free shipping.
The Microsoft ZJA-00001 Arc Mouse features: a thin, arc-shaped ergonomic design that folds together for easy portability, snap-in microtransceiver, and uses inexpensive 2 x AAA batteries.