Hi wysiwig,
It must be really difficult to work all this out when you are unfamiliar with areas. it is bad enough trying to work out a high school in the area we live! we are on the lilydale/belgrave line about 25 minutes from the city so thought I would put in my 2cents worth.
The zone thing is confusing. it is my understanding there is no such thing as a boundary. It is more about going to the closest school to where you live. it seems to vary across the suburbs also. I have heard that in some of the inner city suburbs there are specific "zones" but at DD's school about 4 years they applied to DEECD to put a ceiling on numbers as they did not want to get any bigger. So they got approval to not advertise and to actively discourage people from enrolling if it was not the people's closest school. I got the impression that they weren't allowed to apply a "zone" but it may be possible closer to the city where there is a higher density of population. But as you say, it is strange that you never see these children!
In high school, they seem to be able to enforce the "zone" much more. AT the school DD will be going to , you have to prove you are a resident of the area every year and they don't guarantee enrollment if you are not a resident.
So to your specific questions, but I am only familiar with eastern suburbs so can't help much. Anywhere in from Box Hill toward the city is unlikely to be have property much cheaper than Camberwell. So that means you need to go out between Box Hill and Ringwood. But that will extend the travel time on the train to more like 25 minutes.When those areas were developed in the 1940's to 1960's there were lots of 3 bedroom homes and now they are knocking many down and building 2 or 3, 2 or 3 bedroom units on one block so there are lots of options.
As for schools, as N2L says Blackburn has developed a good reputation. Box Hill is good but has a selective entry component so difficult to tell how good the "normal" stream is as you can't separate out the selective entry.
Another option is Doncaster. If you are close to the EAstern Freeway, it has a bus lane and the bus trip to the city is really quick. Also you are then close to Eastlink for work in the south east. (I think I remember you are needing work in a specific industry) There is a good high school in Doncaster, doncaster east I think it is.
Perhaps you could go to a few open houses in an area that meets the criteria and just see if it is option for buying or renting. Moving out of Camberwell to a bit further out, sooner rather than later, might help you get some money together for a deposit.
good luck. schools are a difficult enough decision without having to factor in moving as well.