My advice: do not buy one of those purpose built cold brew makers. IMO they make worse cold brew than a simple 2 L mason jar and some coffee filter bags.
My recipe:
This makes a cold brew concentrate which can be stored in the fridge for up to 2 weeks. For drinking, dilute with water at at least a 1:1 ratio, if not more (i.e. mix 100 ml cold brew concentrate with 100 ml water).