If you are crusing to a lot of places and are on a budget (which is to say just about everyone), you are looking for ways to save buck or two.
We have found a great source of courtesy flags to be:
Buy US Flags & Flagpoles at United States Flag Store
They sell 'stick flags' that are 18" by 12" for $2.20 each (cheaper if you get more than one the same). You remove the sticks (my wife won't throw them out since 'we might need them some day') and sew a piece of light line
that you pass through the slot. If you want to know why you sew them I will tell you about the Puerto Rico flag at the bottom of the harbor (they don't float well).
They are not as good as the ones from a marine place that typically cost $15 to $25, but will last for a month or two. We will buy extras if we are going to be in a country for more than a month. They don't have every country so you may still need to make or buy a few. We bought a few extra British red ensigns and used them as starters
to make flags for countries like Tonga and Cook Islands. Ask your sailmaker for some spinnaker
cloth scraps in red, green, blue, yellow, white, and black for making flags.