If you're buying from within Facebook, what you're seeing is normal. There was a thread about this during the last gold sale and Mike posted this:
"Mike and Bug wrote
1 month ago
I'm pretty sure those "transaction fees" are only for mobile phone payments, and only in some countries.
These fees are unfortunately added by your mobile network operator (not by us or by Facebook), and in some countries those companies seem to charge a lot, although the example above for Australia certainly seems extreme!
Wherever possible, we recommend using our PayPal option, which has no additional fees, and is of course very secure."
Source:
https://www.fairylandgame.com/fbfairy/forums.php?tid=157531
