Food can be had very inexpensively so I guess you were either drinking non-stop or were dining at high-end places? I lived there, albeit five years ago, and pints (which aren't real pints) were averaging about $15 SGD, so about £8.50. Maybe they're a tenner nowadays. The hawker centres have delicious food at comfortably below $10 SGD. In any case, splashing out on the first day isn't the worst thing, you can always scale it back from there if necessary.
But you are absolutely spot on though: It is expensive for some things, booze (crap booze at that - they somehow love Carlsberg there) being the main one. When I lived there it was on a work rotation from Europe and my accommodation was paid for and I was getting about £80 a day in living expenses, so thankfully I didn't really need to give a second thought to most prices. However If I was living there long-term, paying my own way on a modest wage I'd give up the ale completely.