I self-published through
www.createspace.com, which automatically posts to Amazon (got my first sale through them last week! Yay!) I already had an ISBN and LOC # through a small publisher, but you can also get the ISBN through them; a google search will get you the info to obtain a free library of congress number.
My only outlay to createspace, since I had the isbn/loc has been the expense for the proof copy and then the actual books I purchased to sell. They also have some good resource information on their site.