document.forms['cost_calc_form'].elements['years'].disabled = false;
document.forms['cost_calc_form'].elements['makes'].disabled = true;
document.forms['cost_calc_form'].elements['models'].disabled = true;
document.forms['cost_calc_form'].elements['makes'].length = 0;
document.forms['cost_calc_form'].elements['makes'].options[0] = new Option('Make','');
document.forms['cost_calc_form'].elements['makes'].disabled = false;
document.forms['cost_calc_form'].elements['models'].length = 0;
document.forms['cost_calc_form'].elements['models'].options[0] = new Option('Model','');