Manamorphose costs 1

/

to play, which means it has a replicate cost of 1

/

granted by the Djinn. Let's say you have 3

available. You cast Manamorphose and have enough mana to replicate it twice. The end result is that you now have 6 mana of any combination of colors in your mana pool and you have drawn three cards. There is no infinite draw combo here. The replicate cost is only paid once, when the original spell is played. You can't pay 2

to play and replicate Manamorphose once, let the replicate copy resolve, then choose to replicate again.