I was happy using Just Mayo brand vegan mayonnaise from Walmart, but then it disappeared and came back online only at a much higher price. This motivated me to come up with my own vegan mayonnaise, and I'm very happy with the results!
Place in jar or measuring cup:
1 cup plain, unsweetened soy milk (I use WestSoy)
2 cups vegetable oil
1 tsp. salt
1 tsp. sugar
1 tsp. Dijon mustard
4 tsp. apple cider vinegar
A pinch of black salt (kala namak)
Blend with an immersion blender until emulsified. Store in the refrigerator.