To my understanding the yellow body rx8 injectors are a plug and play upgrade as per the FAQ/WIKI. I checked ebay and people want a decent chunk of change for these used. I thought I'd check remanufactured from vatozone. Advance Auto Parts lists these same yellow bodys here:

Buy AUS Injection Remanufactured Fuel Injector MP-56021 at Advance Auto Parts

Remanufactured by AUS Injection. 49.99 on their website, but I found them on Amazon for 34.40 a piece with free shipping:
AUS Injection MP-56021 Remanufactured Fuel Injector : Amazon.com : Automotive

Is this a good idea? >$140 for injectors is very tempting.

 

I got mine on one of the RX-8 forums for $60 shipped. Those guys are ditching these yellow injectors left and right for the bigger versions. The trick with those forums is finding a set of 4, they are usually sold in pairs.

 

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I bought 2 pairs from 2 members and had them cleaned and flow tested locally. Mine were about $80 for the set of 4 shipped to Canada.