I created a module I am also using both in rails and for some batch processing outside of rails. In order to ensure my data was formatted the same with both environments, I needed to figure out how to get access to the active_view helper number_to_currency outside of rails. Here is how I did it:

require 'rubygems'
require 'action_view'

def number_to_currency(number, options = {})
  ActionView::Base.new.number_to_currency(number, options)
end