I got a pulse oximeter from ebay, including a probe, for under $300.
Ohmeda Biox 3740 Pulse Oximeter
2400 baud, 8 bits, 1 stop, no parity
and in the ASCII setup, i have to check the "force incoming data to 7bit ascii"
some sample outputs (live output is once every 2 seconds):
:SaO2= 96 PR= 78
:SaO2= 98 PR= 80 ** LOW QUALITY SIGNAL
:SaO2= 97 PR= 81 ** PROBE OFF PATIENT
:SaO2=--- PR=--- ** PROBE OFF PATIENT
OHMEDA BIOX 3740 PULSE OXIMETER
TREND DATA OUTPUT
12 SECONDS PER DATA POINT
:SaO2= 98 PR= 64
a site with information on connecting medical devices to computers
Mac OS X and Linux things