. . . this can vary from $1.50 for a regular medium coffee to roughly $3.00 for a cappucino. To say nothing of all the other stuff they throw at you (latte, etc.).
At 0.71, you're safe (around here at least) in using that phrase - "Less than a cup of coffee at Starbucks!"
Although - and I'm no expert - could using Starbucks name in an ad create any trademark or copyright problems?
Just a thought.