They have a long plan with Nunez so they dare to charge a high price. I'm sure Liverpool have reasons for that, the potential he has lured Liverpool to sign him for quite a long time. But surely with that Nunez has to pay with the game he deserves, which can be more convincing Liverpool did not choose him wrong.
If look at his performance with Benfica, it's not bad, even Nunez has become one of the best players in the Portuguese league this season. So I think nunez will pay Liverpool with his performances to match
On the other hand, Darwin Nunez has contributed 10 goals in UCL competition with his team, it's stunning. Besides that Liverpool are thirsty for the UCL title, if there is an agreement between liverpool and nunez, so liverpool don't have to worry that nunez will get used to the UCL competition and will quickly adapt to the premier league with liverpool