Cost of Living in Oslo

I've been there in summer. I don't understand why the rate of walkability is bad, that is ridiculous. People are friendly and polite, if you want to find a job is easy, although opening a bank account to get your salary can take two months. There are plenty of coffees, restaurants and bars, often you need to book in advance (more if the weather is good), and they will rip you off. I knew this, and I went there with the plan of no-eating out, no coffee-out and no-party, but even the supermarket is super expensive.
It is a beautiful city, nature around it is amazing. Social rules are different, as they are in every place, so you should inform yourself before living there. Everybody speaks English and learning Norwegian is easy.
In September it starts to be too cold for my taste.