Instead of a card I want to get my girlfriend an expensive present for her birthday.
That seems nice. What makes you want to give her a present and not a card?
I think actions speak louder than words.
It is good to give people gifts and not cards. A gift can be more useful and show you really care about someone because you have to put though into it.
I have put a lot of thought in the gift.
That is good, gifts are more personal and makes the person feel like you actually thought about they want. I am sure she will appreciate it.