Don't listen to these cheap ass guys... In my opinion this would be like paying for a night in a club or something. Paying for fun and good times.
You don't give her money, you pay a little extra for you to enjoy the trip even more and potentially get a nice friend or even better girlfriend.
No reason to save up to be the richest man in the graveyard, if you know what I mean. Spend your money on things that can improve your fun/happiness or whatever.
And if she is into you, she'll will probably see it as a really nice gesture and a sign from you that she is worth it.
Well this is me, I'd rather spend money on taking my friend with me clubbing, to movies or on vacation for that matter if I have the money, so that we can have a laugh, experience things together and share good memories. Than I would want the newest phone, pc or whatever.
Do what you feel like man!