The price is $15.
You may purchase your serial number through the Kagi store using the link below. Kagi will send you a serial number by return email within an hour or two at most.
If you have any difficulty with the Kagi store, you may also purchase your serial number using PayPal. The PayPal shopping cart is secure and easy to use. After your purchase is complete, you will receive an email with a serial number within a day or two at most. While you are waiting, continue to use the game in trial mode.
Questions? Contact the author, Steven Estrella, at firstname.lastname@example.org.