Alvarez is a pretty decent player, he is young, he scored 19 goals for City last season, he is a world cup and copa winner and he played a good part on those teams. Do i think he's worth 90? Nope.. Do i think he's worth 60 or 70 in this market? Probably.
Edit - and as Burnsy said, i think they will be paying in installments over the next 3 or 4 years