You should check out Kings Park, Cranbourne, Wallan, Hoppers Crossing and Jacana. They all have a median of between $350,000 to $360,000
For the most affordable suburbs in Melbourne I'd recommend Clyde, Clyde North, Pakenham, Frankston North and Cranbourne West. You can get decent 3 bedroom homes for around the $300-350k mark.
Not Clyde North anymore used to be :( , now its mid 500's which is still pretty low