The game may be purchased for US$10 with any major credit card. US dollars may not mean much to you, so we have provided a link to the Universal Currency Converter to give you a rough idea as to how much your credit card will be billed:
Note that your credit card may not be actually billed by this generated amount, it depends on bank charges, exchange rates and many other things. It should serve as a guide however.
The secure credit card transaction service is provided by RegNet - The Registration Network. The product ID for Flow is #7631 and the author ID is #2513 (ned Productions). You will require a web browser capable of secure web transactions (recent versions of MSIE and Navigator qualify as do a fair few other browsers)