400 a week won't get you a 2 or 3 bed, 2 bath property close to the city. But Box Hill has a lot of what you're looking for and prices have recently dropped to about 450 p/w you might be able to find something for less there. For 400 and under for what you want, you're unlikely to end up within 5 or 8km of the city. Footscray isn't as safe but you'll find what you want for that price.
Otherwise, try Reservoir or Preston in the Northern Suburbs.
Or Bundoora if you're willing to spend at least 60 minutes getting to the city it's a much safer area.
A lot of this depends on how safe a suburb you desire.