Not free, but inexpensive compared to actual courses: David Burch of Starpath has a coastal navigation book, plus a couple books of navigation exercises based on NOAA 1210Tr (Block Island Sound) and 18465Tr (Strait of San Juan de Fuca) training charts. All of these are available via Kindle for less if you find that format usable, or in dead tree versions if you don't. Edit: Expect to pay $50 for paper, or $30 for Kindle, to get the main book and one of the workbooks. Training charts themselves are only $10-15ish.
I have the main book and the 1210Tr workbook/chart combo, and once I'm done with the fire-drill busy season of Christmas, I'm planning to work through them.