Geez injectors, that's where my nightmare started! 😢 When you say one of yours has packed up, what do you mean? Mine worked fine but they were leaking fuel - no way to fix that. But you can get the filter basket replaced at Bosch Service Centre - you can also get your injectors tested there for spray pattern and capacity.
As for replacing, the standard ones are 370cc, and as mentioned above, are R2000 each from Nissan. I eventually had all mine replaced, but that also involves remapping the ECU to cope with them. Both routes are expensive, but at least with the second option, you can up the boost and get more power (if your exhaust gasket can handle it) 😀