My statement still applies if you buy a set of 6 plugs. One bank/side of the engine fires central electrode to ground electrode, the other side fires ground electrode to center electrode. If only 1 is platinum/iridium, one bank will wear faster than the other. The wear occurs most at the point from which the spark emanates, just like welding, the metal flies from the origin to the destination.
Again, since your funds are limited, make sure the IAC/EGR is a source of problems. The DPFE sensor is often a failure point, not necessarily the EGR valve, though it may be clogged. IAC may be clogged too. If you feel frisky, take both off and clean them but don't replace them just because they might be the source of the issue.
I know I'm sounding harsh but I've been down that road. You think you're guessing right but a few hundred later and you don't have a solution to the problem. Take the smart approach, get a diagnosis and you'll have saved money and gained intimate knowledge on how the engine works