Welcome to the 'Bolt Mag!
Have you removed the head to determine how far the crack extends? Without knowing more details on the existing condition of the engine, it may be cheaper to just acquire another 250, but really can't tell without more info.
Just judging from the picture, it looks like the crack may be through and exposed to the coolant passage, which would make it a must do to repair if you want to retain the engine. There are a number of ways, which I will leave to others more experienced in the methods and success or failure stories to discuss, but here again the question to ask is what is the value of the block?
Also just IMHO, but that crack would have been readily identifiable before the paint was applied. If whoever worked on it before you missed or ignored that issue, I'd be digging into the engine more to determine it's actual condition before trying to put it back to work.
