Cost effectiveness is directly tied to individual application. For me it's cost effective to spend several hundred $$ on a good set of cutters. I find the finish is far superior to anything you could buy in router bit form. Additionally I buy 1-1/4" cutters as the increased diameter improves quality over the smaller sized 3/4" bore cutters. But I make a fair amount of doors so the ROI is pretty good. For someone making a dozen doors a year, well probably not such a good investment.
I think a better analogy might be something like using a 4-1/2" saw blade on a 10" cabinet saw. Sure you could do it, and it may save you a couple dollars, but it's just not a practical idea. The performance benefits of using the larger dia. blade outweigh any cost savings.
JeffD