So basicaly it's like this, will be impossible to keep paying for the game with this high USD curreny at my country, basicaly 1 USD = 4 R$. The suggestion are simple make a payment method based at brazilian currency for the called Latim América.

If you base for Latim América using Reais will be easy for people pay the game that are outside from US and still live in América plus will get more players from this places.

Just to make my point, Blizzard let us pay using Reais which go "cheap" for us and that's why a lot of people keep playing the game (have more than 10 years and still get new players).
I see two easy ways in making it possible, can use the PSN account registration and or use the billing info for it (can even put like locked to bank CC information when check it).
Other way would put to sell the time card with a offical release and locked price like Sony and MS have done with their Cards for PSN and Live.