Agreed with the others, theres no rush to purchase a stethoscope now. Our stethoscope was provided to us under a generous donation from an alum. Not all schools provide one of course, but if you have medically minded family members/friends, there's a chance that they might give you one too. If you aren't lucky enough to get one for free, you can look for one online at medical supply stores where they are usually discounted. When I was shopping for one, a store even provided free engraving too. As for which stethoscope, the Littmann Cardiology III by 3M is the most popular with medical students and I would even say most residents/physicians too.
EDIT: ew SDN adds adwords now