Amazon offers Prime members the Lutron Maestro 150-watt Digital Dimmer in White, model no. MACL-153M, for $18.35 with free shipping. (Non-members can spend $49 or more to qualify for free shipping; otherwise, shipping costs $6.63.) That's the lowest total price we could find by $7. (For further comparison, we saw two of them for $42.86 in May.) It features multi-location dimming for up to ten locations.

Update: The white dimmer has sold out, however Amazon offers an identical dimmer in Almond for a slightly lower price of $18.11.