You dont need a yoghurt maker. When I went to buy one once the shop assistant was Iranian and was amazed at the idea. She told me how to make yoghurt: heat up milk to just under boiling;let it cool to tepid ;take a spoonful of the milk and mix with a spoonful of live yoghurt (how much you put in varies depending on how much milk you have and how you want the yog to come out);mix back into the tepid milk and stir well; put the lot in a AIRTIGHT container and leave in a warm place. 12 to 24 hrs later you have gorgeous yoghurt. If you live in a cold place you can insulate your container (wrap it up in a blanket) I make my yoghurt in a crockpot,once at the right temp, turn it off, wrap it up(unplugged) and leave overnight.
The yoghurt will start tohave a liquidy bit after a while; you can just stir it back in or strain through muslin for a few hours to make greek yoghurt, which is thicker and tastes sweeter.