450 Euro/month should be enough.
Mozambique is considered to have a low living cost
The Expat Arrivals page on living costs in Mozambique should give you some idea.
Note that it'll be too expensive to live on your own and eating out in Mozambique can be pricey, so you'll have to save money where you can.
Which area in Maputo would you like to live in?
Do you have people that you can live with?