converting dried measurements to soaked measurements
250g of canned black beans is about a cup of soaked/cooked beans, which is the same as a drained 15oz/425g tin. 

The volume of beans increases from 2-3x. It is probably closer to 3x for black beans but I'm not certain.

So I would cook up about 80g-90g of dry beans, I think that will get you a bit more than you need without a huge waste. 70g would probably nail it but if I'm wrong you would be short. And I'd take notes on what the weight change is for future reference :-).