The OEM headers are a good design but not so good that it can't be improved on.
For example, while I have no experience with the Gen 3 motor, I know that for the
Gen 2 3SGE the Fujitsubo Super X system is a much better design than stock. It retains the stock 4-2-1 format and is all stainless with larger diameter
equal length primary pipes, much smoother welding inside the pipe branches and is all mandrel bent (unlike the stock header).
Even fitting this on it's own can give gains you would notice.
I agree that buy them new they are certainly a lot of $$$, but unfortunately that's just the way it is - good stuff costs.