The normal order would be "I'll (do something) for you":

I don't usually give my number out to people I've just met, but I'll make an exception for you.

But you can also use the order in the example above. People use this expression when they're doing a special favor for someone:

It's twenty dollars, but for you, I'll cut it down to fifteen.

You can sound generous and helpful by using this expression. But you can also sound a little sneaky or dishonest.