If you were not going onto nursing school, I'd say stick with a cheap one but since you plan on moving on, in the future, if Mom wants to buy one for your birthday, I say go for it and get a better one.
My Littman Classic II I love. It was under $100, and it can be found in PINK!

Once I graduate I plan on moving up and getting a better Littman.
Word of warning, keep your eye on your scope, they tend to grow legs and walk away, never to be seen again.
Oh you can get a Littman in most scrub stores, some medical supply stores, on line, and in catalogs.