Surprising there wasn't more feedback on this question. Aside from some of the precision parts, the most important component in FTIR is signal analysis done entirely in software. I'm certain some other issues (besides position control, like thermodynamics) are important. For ATR FTIR we used liquid-N2 to cool apparatus which may be a general requirement of FTIR. This question prompts me to investigate further.
Perkin-Elmer sells replacement KBr beam splitter for $3950 so I begin to see the problem with purchasing the optics separately.