Color -> Greyscale

This thread began with a simple question: "How does one convert a color image to greyscale", but then devolved into a discussion of ICC stuff and vehicle ignition switches. I would like to ask the question again, with some specifics:

I have a large number of digital color images that will be pasted into a Pages book manuscript and, later, printed and hard-bound. Many of the images were scanned using the standard printer-scanner settings that default to color, and others were photographs taken with color cameras.

Some of these images would best be shown in the book as greyscale pictures. But when I send snippets of the manuscript to the publisher, they tell me that--even though I've used a "quartz filter" to create a picture that "looks" like greyscale on the screen and prints as a greyscale, those images have 'color components' in them and therefore the price I pay for the printing will increase. The publisher never gives me specifics about what constitutes 'color components' nor how to eliminate them.

So, without telling me to undertake a technical education in color management and fancy graphics software, please tell me if there any simple way for a novice without a lot of money for fancy software to convert these color images to the old-time black and white photograph-like images?