$ phantomjs ./ec2.js ./config.json

config.json

{
  "t1.micro": 0.5, // 0.5 * 24 hours * 365 days / 12 month
  "m1.small": 1
}

ec2.js

/*jshint evil: true */
/*global require,phantom,jQuery*/

var page = require('webpage').create(),
    system = require('system'),
    fs = require("fs")
    ;

var file = system.args[1];
if(!file){
  console.log("Usage: " + system.args[0] + " <config.json>");
  phantom.exit(1);
}
var conf = fs.read(file)

page.open("http://mikekhristo.com/ec2-ondemand-vs-reserved-instance-savings-calculator/#" + encodeURIComponent(conf), function(){
  var result = page.evaluate(function(){
    // use eval for commented JSON
    eval("var conf = "+decodeURIComponent(location.hash.substring(1)));
    var targets = [];
    Object.keys(conf).forEach(function(key){
      jQuery('input[name="num_' + (key.replace(".","_")) + '"]').val(conf[key]).trigger('keyup');
      targets.push(key);
    });
    var result = "";
    targets.forEach(function(key){
      result += key + " : $";
      result += jQuery('input[name="num_' + (key.replace(".","_")) + '"]').closest('tr').find('td:nth-child(3)').text() + "\n";
    });
    result += document.querySelector('#current-amount').textContent;
    return result;
  });
  console.log(result);
  phantom.exit(0);
});

result.txt

$ phantomjs ./ec2.js ./config.json
t1.micro : $7.30
m1.small : $47.45

                 

                        With on-demand, you currently pay:

                                $0.00 upfront
                                $54.75 monthly