It is quite easy to make your own yoghurt. All you need is a good quality yoghurt with active yoghurt bacteria as a starter, and some milk. The usual yoghurt making recipies then require you to warm up the milk to a certain temperature, add the yoghurt and keep the yoghurt warm for several hours until it sets. I used to be quite successful with this method but I have found that the yoghurt sold in Australian supermarkets doesn't work quite as well as the yoghurt I used to buy in Europe. Not sure why that would be - is the yoghurt too old? Do they process it differently? Maybe it is me who is doing something wrong? Then there is the issue of making sure that the milk is exactly the right temperature - too hot, and it will kill the yoghurt bacteria, too cold, and the bacteria won't multiply and therefore not turn your milk into yoghurt.
I am now using a small yoghurt maker which requires no electricity. This is working really well for us and has resulted in major cost savings, too.
The system is quite a simple one and you might have all the ingredients to replicate it at home without having to buy any commercial units, although the one I bought was not very expensive either.
It consists of a large thermos with a small perforated holder tray placed inside. The thermos gets filled up to about half with boiling hot water. The initial batch of yoghurt is made up from a small bag of powdered yoghurt which is available from any supermarket. Made that way, 1 kg of natural yoghurt costs about $3.00. This is around half of what you usually pay for yoghurt off the shelf.
The yoghurt powder (which is a mixture of milk powder and yoghurt cultures) is mixed up with cold water in a 1-litre jug and then put onto the tray inside the thermos. It stays there for between 6 and 12 hours, depending on your time frame and how strong you like your yoghurt.
I found that the resulting yoghurt is very fresh and can easily be used as the basis for another batch of yoghurt, which is what I do. If you need a fresh starter yoghurt, you can either buy another sachet with yoghurt powder from the supermarket or purchase fresh yoghurt cultures from cheesemaking suppliers.