The Lab (2948 16th Street) hosts its annual Post Card show beginning Friday night. For this small-format show artists submit a box full of work-- all priced below $30. In the past works by artists like Misako Inaoka have been spotted for $20. Expect a wide variance in the quality, but some real gems if you're willing to dig (and get into it with the rider of a fixed gear, or two). Open to the public starting Friday at 6.