If you want to ho high end, facilities I worked at usually had Sprague stethoscopes around.
Most nurses, however, myself included, wanted a personal stethoscope that no body else used for hygiene purposes. Some bought Sprague but most went with a standard double belled unit that cost under 20$. These things get banged around a lot and unless I was working in an area like stage 2 cardiac/intensive care, the cheaper ones will get the job done.
QUILL has a Briggs/Rappaport stethoscope in their medical arts catalog that I have opened on my lap right now for 14.95.
AAAAAA+++++ company to work with. Free, fast shipping and reasonable prices.
Make sure you can protect it from elements and wipe off the bell with an alcohol swab if you use it on humans as well as your chickens.
It is always handy to have one around in case somebody has a respiratory illness and you want to check the lung involvement.
microchick/retired nurse