Mediocre roads indeed, but you can manage to get around the city by public transport. While public transit can be sometimes late, or some buss lines use old busses. it's A+ compared to US public transport, but not as great as the London or Paris (tho the metro is newer and cleaner than Paris). Public transport card for all lines for 1 year is 365 levs - 185 eur.
Rent prices currently are on the high end and can run you between 300-500 eur.
For food, i personally eat take out twice a day and over the last few months my average spend for food & drinks is ~ 300 eur.
If someone has other questions about Sofia, feel free to e-mail me or comment here :)