The coffee only cost me £2 (from a street vendor in London), so I could have afforded a Blueberry muffin with the £2.66 change :) I like to think SBD has a natural cap. Some sort of function of $1 and the 10% per annum interest rate. But with interest rates around the world around 0, it could certainly go higher than the current $1.30ish price tag...