Baptism gift

My daughter is being baptismed tomorrow - with her cousin, my sis's daughter.  I completely forgot that I should be getting something for my niece until now.  I'm going the monetary route, but I have no clue what's appropriate for an amount.  I know some people will say to go with what you can afford, but I don't want to end up giving my sis's kid half what she gives my child - you know? 

For those of you who have already had a baptism, around how much money did you get from guests for your LO?  Not sure if this matters, but I'm in the northeast where a pretty typical wedding gift would be $200

tia