Fish question..Black Moors?

My friend bought me a fish bowl and two goldfish for my birthday. Yesterday, one of them died. So I am thinking, to make my only fish left living experience better is to buy a bigger living environment, a tank. But I don't know how big It will need to be. Also, I want to get a couple of Black Moor fish too..but I dunno how big they get and how much space they will need. Can someone help me with tank size and how much it'll cost me? I live in South Australia.