Starbucks: they don't charge $2 a coffee. I would only ever get a drip coffee and I think it's around $3, most people who are going there get drinks in the >$5 range. Plus they have a lot of traffic - more customers = less wages required for each drink
McDonalds: They charge less than $2/coffee. They charge less than $8 for a breakfast. They make their money on super high volume.
Your vision: you're enjoying lingering, enjoying the sun. You're enjoying the floor (patio) space, which means you can't have high volume unless you have a huge space, which wouldn't work with your "little shack" concept. Unless there's a nearby park or beach with free barely limited space, while also still having enough traffic to stay busy. Very limited spots that can work.
(so as with most issues regarding our urban spaces in north america, what we need to make them better is more density. :)