How much to press and alter gown?

[So_happy]

I fell in love with Maggie''s Rebecca today and the shop I found her in offered either 20% off the gown or free alterations and pressing. The 20% off will save me $110........will a 3"hem (no bead work etc exsist on the hemline so I presume it would be a straitforward task) and pressing cost more than that?

And, more specifically, how much should those two things cost in case I find the gown elsewhere for less money and want to get the alterations done elsewhere?

I''m in the Northeast area if that matters.