If you buy dozens and dozens of dollars just to be able to bring a few days, a little longer wear and tear, almost no value to keep.
I think since it's a girlfriend with long-term plans, spending a few hundred dollars should be considered affordable, save up a little, and according to my estimation it shouldn't be more than three or four hundred. In my experience, your girlfriend will be very touched after receiving it, and she will always remember it, which is definitely more touching than buying a big diamond ring when you get married.