O2 sensors for '97 328

I have a 1997 328iC that is throwing catalytic converter codes along
with O2 sensor codes.  Both me & the local converter expert suspect the
problem
is actually more the O2 sensors than the converters, so I'm going to try
replacing them first.  The problem is that BMW wants $200 + each for 4 of
'em!
That makes the sensors worth over $800!
	Does anyone know where I can find some after market O2 sensors at a
reasonable price?
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Jinks ('86FXRS, '07 FLTR)
#64
Remember, "No good deed goes unpunished"