The Spanish giants spent €96million in enticing former Manchester United superstar Cristiano Ronaldo from Manchester United in June 2009 and Serrano thinks Real's president Florentino Perez could break the €100m-mark to purchase Bale from Tottenham.
Marca is widely regarded as the voice of Real with the Madrid-based newspaper regularly writing articles in support of the capital club.
"I believe that Florentino Perez is prepared to pay what it takes but there are some figures that are unattainable," Serrano said on Monday.
"He is not going to double that amount (paid for Ronaldo) or even go as far as €150m but €100m Florentino would be more than willing to pay."
The rumoured figure would make Bale the world's most expensive footballer and would be a welcome boost to Madrid after rivals Barcelona spent €50m to bring Brazilian star Neymar to the Nou Camp.
"There's no doubt the pressure Florentino Perez is under is enormous," Serrano said.
"Barcelona blew the transfer market open by signing Neymar, a player Madrid was also trying to sign, so Real Madrid were left with no other options other than signing Bale.
"They have to buy the best player available who doesn't play for either Real Madrid or Barcelona, and at the moment that is Gareth Bale."
While Tottenham chairman Daniel Levy is very reluctant to sell the Welsh star, Bale's representatives have reportedly asked the English Premier League club to let the 24-year-old leave, although the pressure is still on Real to make an offer that cannot be refused.
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