[e1f]

$(document).ready(function() {
    var globalSum = 150;
    var price = 0;
    var page_val = 0;
    $("#page_count").keyup(function () {
        page_val = $("#page_count").attr("value") * 30;
        $("#result").attr("value", globalSum+parseFloat(page_val));
    });
});

так?