Despite Amozon, Google etc...
it appears the book should be free -
http://forum.nasaspaceflight.com/index.php?topic=30393.15
" Here's the VERY LAST SENTENCE IN THE BOOK:
Quote
Redistribution of this e-book is permitted, so long as it is distributed for free"
PDF available
In which case maybe some revisionism and backtracking is going on! -
http://www.galactanet.com/writing.html (Andy Weir's page)
"...The Martian:
The Martian is going to be published in print by Random House. The hardcover edition
is scheduled for release in February 2014. Until then, it will not be available in
print or digital form. The Audiobook is still available. ..."