I think that is expensive too - I wouldn't spend 155 baht on McMuffin b/fast much less any b/fast. I think though that USD4.90 is the norm for this in a Western country. But they have higher purchasing power parity.
Propensity to spend does not always correlate with how much you earn, though. I know people who earn and burn and people who are thrifty. I personally don't go crazy even with company's money. Not too little, not too much, just nice.
I am always curious on how people plan for retirement in Thailand. There seems to be a reliance on children. I hope to be self-sufficient.