I had a guy at Pep boys tell me it needed both cow sensors replaced-$600
Actually he meant O2 sensors.
I'll start here. you DON'T need both O2 sensors replaced. One MAYBE.
To understand why you need to know what the 2 O2 (or Oxygen) sensors do. There is one before you catalytic converter (or cat for short) and one after it. The one before it (also called the front or upstream sensor) is the important one. It is a wide band O2 that monitors your engine and lets the ECM (engine control module or computer) know how successful it was measuring the air fuel ratio based on other sensor inputs. Lean means the ECM didn't add enough fuel. Rich means it added too much.
The second (or downstream) O2 is far less important. It's job is to let the computer know if the exhaust output from the cat is within acceptable levels when compared to what entered the cat as measured by the front O2. If the difference is too great, it sets a very specific engine code. The presence of this code would mean your cat isn't working and has failed or the rear O2 sensor has failed and is not working.
P2187 is not the code for a failed cat. Therefore, your rear O2 is fine. Just as important is a key line in the image you attached:
...PCM detected that long term fuel trim for bank 1...
First, while a PCM and an ECM are not the exact same thing, a PCM and an ECM will control the engine and can throw the same codes. (I can get into what makes them different but that's not important here.) So this is saying the ECM detected that the long term fuel trim is lean. The key is Long Term Fuel Trim (LTFT).
You have probably heard your engine will "learn" how you drive and adjust over time accordingly. That's the LTFT. As you drive, the ECM is recording data from its sensors to see what it is "guessing" how much fuel to deliver under various conditions. It compares it's guess to the report from the first O2 sensor to see how close to "correct" it got. If it sees that it was lean, it will remember to add fuel next time those conditions are met. If it's rich, it will remember to subtract fuel next time those conditions are met. It saves this information and averages it out over time. This average is stored as a LTFT entry. (There is a short term fuel trim...STFT...also, but again not important for this discussion.)
Now, the O2 sensor does not interact directly with the LTFTs. If the O2 reading is rich, the ECM will lean or pull fuel with the LTFT to try and get the reading from the O2 to match what it is trying to target. So while the problem COULD be a bad front O2 sensor chances are you would have other codes as well as the O2 would always be reading richer than the engine is actually running which is what would be required for the ECM to keep pulling fuel to such a degree that the LTFTs would be set very lean.
Thus this code is very specific to the value of the LTFT which is calculated by the ECU. The code is saying the LTFT value is too lean. What causes this is something is happening to cause more fuel to get into the engine for a given amount of air than the ECM is expecting even though the ECM is trying to command less fuel OR the ECM is being told there is too much fuel when there really isn't. The latter problem is the O2 sensor but the former problem could be a bad High Pressure Fuel Pump (HPFP) or a leaking injector. I don't know if the Redline can have the HPFP go "bad" and not lower pressure when it is supposed to or not. Not that familiar with the system. BUT, if there was more pressure in the fuel rail than there should be, the injectors would flow more fuel than the ECM would think they should be flowing at lower RPM levels (like idle or deceleration) and thus causing a rich condition that the ECM would try and fight by pulling more fuel through the fuel trims. Over time the LTFT would get set to a very lean setting and trip this code. The same basic thing would happen if an injector leaked (meaning leaked fuel into the combustion chamber when it should be shut off). The ECM has told the injector not to spray but fuel is leaking into the cylinder anyway thus making the mixture too rich and again, the ECM counters with the fuel trims to lean it back.
Front O2 is easy to replace though even on your own. Unplug the sensor and unscrew the O2 sensor form the downpipe (on a cold engine) using a 21 or 22mm open end wrench. Once you break it loose, you should be able to unscrew it with your fingers. The wiring harness from the O2 can be a bit tricky (it will wind up and try to screw the sensor back in as you are trying to get it out. LOL) but it's pretty accessible from the engine bay. I think the O2 costs less than $90. The rear possibly less than that...but you don't need that one changed.
Injectors and HPFP are far more expensive and not so easily swapped out. Thus, you may want to start with the front O2 and see if that is the culprit first. O2 sensors can go bad and if you haven't changed yours, it could be time. It should NOT cost $600 to change both O2s. It should be parts plus 1 hour labor even if doing both (you do need to get under the car to change the rear one but it is easily accessible). Under $300 easily even at $110/hr labor rates.
Since I haven't posted it in a while, I'm attaching the closed loop cycle image I made a few years back in this reply. In a car with a narrow band O2 (like the base model LE5) you have open and closed loop. I believe (and please, someone correct me if I'm wrong) the wide band equipped LNFs run in a form of closed loop all the time. Just one change, on the intake side of the loop, where it talks about Short Term Fuel Trims...note that Long Term Fuel Trims are factored in here at the same time as well.