Hamas spent around $30 to $90 million, and poured 600,000 tons of concrete. Some tunnels were estimated to have cost $3 million to construct.
The parties involved in helping Hamas in the construction is a Secret.
Guess the secret countries:
Guess 1: Iran
Guess 2: Russia
Guess 3: North Korea
Guess 4: CCP China
Guess 5: ??