Average price for a Starbucks drink?

That depends on what you're getting. I'll go by Grandes because they're the medium size.
Brewed coffee: $2.25
Latte (no modifications): $3.75
Frappuccinos: Anywhere from $3.65-4.95
Iced Coffee: $2.65
I could go on, but I don't remember every price off the top of my head. The point is, depending on what you get and how you modify it, you could spend as little as $2, to as much as $6.

In uk between 3 and 4 pounds

3 bux