also don't forget that Nismo stuff is only a VERY SMALL part of what is the aftermaket parts available for our car, and not necessarily the best choice, or the most performing.
In fairness, Nismo is also known to get other manufacturers' products and re-badge them (and sell them at a higher price too) examples of this are the exhaust, manufactured by Weldina, the CAI, manufactured by AEM and there's more examples like the coilovers that are manufactured by someone else too (Tokico?)
oh and that cats price is just ridiculous imo, considering you get GREAT cats+plenum packages by very reputable companies such as Crawford or Kinetix for $600... (and they are parts which you can have fun fitting yourself too )