One thing we try to do at Homeschool Connections is keep prices low for our families. For our upcoming Chesterton course, instead of asking our students to purchase 6 separate books, we did a little web surfing and found all six books online for free.
If you'd like to read Chesterton online for free too, here are some links for you:
The Literature Page
G. K. Chesterton's Works on the Web
Librivox (audio books)
Christian Classics Ethereal Library