I lived in Peter a year, and had my own apartment. I also bought my own groceries. I bought mostly imported food and I spent about $20-25 for one week of food.

Rent was $500 (3-bedroom apt), my share: $200
food: (conservative) $30*4 = $120
resaturants (happens to the best of us): $20*4 = $80
Alcohol: Expensive beer at bar: $2*100 = $200

still only $600

what will get you is museums and stuff, unless you are a student. I was a student and got free entry to nearly all museum. The Russian Museum I visited almost every week at one point.