A deal between the two companies could be announced as soon as Thursday, according to people familiar with the matter. Altice is expected to pay $34.90 a share, one of the people said. That would value Cablevision, which has a market value of $7.9 billion, at roughly $18 billion including its heavy debt load. The deal would rank as one of the larger takeovers in a roaring year for mergers and acquisitions.