Buttermilk costs approx $4 for 600 mls. Here’s how to make your own. To 1 cup of whole milk add 1 tsp vinegar or lemon juice (acid). Stir in and let stand for 5-10 mins. It will thicken. Other buttermilk substitutes are 3/4 cup plain yoghurt and 1/4 cup water mixed together or sour cream thinned with milk until it reaches the consistency of buttermilk.