This library provides a basic api to instapaper bookmarks for free by scraping the page
n.b. this is a work in progress, you probably shouldn't use it.
gem install instascraper
require 'instascraper'
i = Instascraper.new('username', 'password')
# load unread bookmarks
bookmarks = i.bookmarks
bookmarks.each do |b|
puts b.link
puts b.title
end
# folder support
folder_bookmarks = i.bookmarks('folder name')
Significantly modified from the original Instascraper.