Build a Website - Enhancement

I need a feature added to my website, basically there should be a place where a person can enter a number between 1 to 5000 and there should be another area where the total calculates automatically. The number you enter should be automatically multiplied by $40.00 USD. Once they get the total I need a Button which says "Order Now" once clicked the person should be directed to checkout. My website is based in Wordpress and uses WooCommerce eCommerce gateway. I need this done within few hours, whether you are going to do this as a plugin or a special script please let me know as far as timing I need this done within 2 hours. Do not bid more then 2 hours time frame you will be ignored.