Lower Gilberton is significantly cheaper than upper Gilberton which has some of the most expensive real estate in Adelaide with some mansions worth millions. A double fronted Victorian cottage in lower Gilberton will set you back between $800k and $1 million. Unrenovated cottages (and there are not many left) are about $650 - $750k depending on the block size.
Depends upon the type of housing. Gilberton is generally cheaper than Walkerville and St Peters but prices vary significantly depending upon whether you are looking at an apartment through to a renovated or extended cottage.