What's the cost of a non-reusable coffee cup?

I had nightmares about missing the bus. We woke up before sunrise. We finished up our cereal and jumped out of the house. The bus ride to my daughter's art class was exactly 1 hour. While she painted, I took my 4 year old and the baby to an organic cafe nearby.

"Could I have a cup please?" I asked the owner. That was after a $30 order, which included 500 ml of chocolate milk in a carton. I wanted to pour it into a cup so that we could walk to the library with less chances of spilling.
"You can have this one, but they have no lids."
"I'd like the one with the lid, if possible."
"They are really expensive. I don't give them out. I sell them."
"How much are they?"
"35 cents."
"That's okay, we'll do without it."
"Not, take it."
"That's okay, you can keep it."
"No, no, take it."
PAUSE.
"Okay, I'll take it." (This, accidently, is a famous, much debated and much rehearsed, line from the famous 2 minute fim I made in graduate school.)

I felt compelled telling the owner that we'd be regular customers from now on, that we would never again ask for a cup, and that her sandwich was nice. I felt like I stole that cup. 35 cents? Really? I felt so bad that I actually brought it home with me. I *am* concerned about the environment, am I not?