(I've posted before elsewhere.) Had a III which I had bought during nursing school for the day I'd graduate, and bought an ADC 603 to use during school several years ago. But recently, after doing a 20-min sound test between the two (having used the Littman III maybe three times) sold it after comparing it again to my $30 ADC 603. (As someone noted elsewhere, the III is heavier, not as agile using it, tight earpieces.)
The $30 ADC 603 is comparable (I think) to the $80-$90 Littman Cardio II (the II is slightly shorter). Yesterday, I held my ADC 603 to the neighboring nurse's Littman II side by side, listened to both, and, again, there was absolutely no difference in sound that I could perceive. So you don't HAVE to spend $100-$200 unless you WANT to. On the floor all you need to tell is the heart is beating, regular or irregular, murmur, lung sounds (cheaper works just fine for that unless, perhaps, you are planning to round with a cardiologist), bowel sounds (gurgles come just fine over cheaper. The trick with stethoscopes is not too cheap, rather than not too expensive. (For instance, I can't hear anything over the disposable $5 plastic scopes they want you to use for MRSA patients.) I'm just going to get another ADC 603 for back up.