Ask some heating & air folks for a couple old transformers or see if they'll let you steal one from an old furnace. Most contractors usually have a pile of old furnaces removed when they install new ones. Some transformers use a 120 volt input while others are 240. If you get one of each you are set. Feed them both with 120VAC and the 120 volt one will give you 24 VAC out and the 240 volt one will give you 12 VAC. Most residential units use transformers with 120 volt primaries so finding a 240 volt one will be the hard part.