Partly this: Number of bits. This attack is almost 2^64, and SHA-1 is 160 bits. All else being equal (big big if) that means sha256 is 102 bits, meaning 362703

Partly this: Number of bits. This attack is almost 2^64, and SHA-1 is 160 bits. All else being equal (big big if) that means sha256 is 102 bits, meaning 362703572709.30493 times more expensive. Or about $16321 trillion USD.