The Brazil international moved from Roma earlier this month for £65million but the Reds boss believes it was a necessity in a small market place, and said there were even more costly options out there.
Atletico Madrid's Jan Oblak was another of Klopp's targets although he proved to be prohibitively expensive.
'Everybody thinks it's a lot of money. It is a lot of money but he could've left for crazy money,' Klopp told ESPN FC.
'The clause for Oblak for example is 100m euros (£89m), so nice!
'The goalkeeper market is different because it's not each year that there is anybody available.
'We didn't know exactly if Alisson is available or not but from a specific moment we realised obviously he is available, and that's the moment when we decided we want to go for him.'