Walmart offers the AcuRite 5" Easy-Read Magnifying Rain Gauge for $3.23. (Amazon charges the same.) Opt for in-store pickup to avoid the $5.99 shipping fee. That's the lowest price we could find by $3, outside the below offer. It's made of weather-resistant acrylic.

A close price: Blain's Farm & Fleet offers it for $3.49 via in-store pickup.

Update: The Walmart offer has ended; however, Amazon still has it for $3.23 with free shipping for Prime members.