I know that 6-8 seat jets are much cheaper, but what size do you have to go for to at least exceed the restroom in a public A320/737 based airline super cramped

I know that 6-8 seat jets are much cheaper, but what size do you have to go for to at least exceed the restroom in a public A320/737 based airline super cramped one? Not that I anticipate buying any jet, but I think that would be the threshold to be worth it to me if I ever was able to.