Lallana moved to Liverpool from Southampton in the summer of 2014 for a transfer fee that BBC Sport reported at the time to be worth £25m.
“At £30 million-plus, the fee does seem slightly excessive but, taking into account his age, 24, and his performance at Southampton, Liverpool won’t be too concerned with making him one of their most expensive signings ever, especially if he is Klopp’s No 1 target,” Cascarino wrote in The Times.
“Lallana, the England midfielder, cost Liverpool £25 million in the summer of 2014 and in Mane they will be getting a better player,” added Cascarino.
“The fee is no more than a reflection of how the market has changed, particularly with the extra money clubs now receive from the new TV deal.”
Mane scored 11 goals and created 41 chances in 37 Premier League matches for Southampton during the 2015-16 season.
The former Red Bull Salzburg winger had a pass accuracy of 81% and a shot accuracy of 52%, and won 26 headers, 77 dribbles and 39 tackles.
During the 2014-15 campaign, Mane scored 10 goals and created 40 chances in 30 Premier League matches for the Saints.
Lallana, who can play as an attacking midfielder or as a winger, scored four goals and created 49 chances in 30 Premier League matches for Liverpool last season.
During the 2014-15 campaign, the England international scored five goals and created 32 chances in 27 league games for the Reds.