my maths is pretty vrot too

but my understanding is the following
WoW month-to-month CC subscription = 12.99 euro (R146+-) *
60 day GTC from RPG bay = R315 (or R157.50 per month)
So a 60 day GTC should be below R290 before it becomes cheaper. To put it in perspective, the R220 GTC's (which were stolen unfortunately) meant a saving of about R40 per month (give or take, depending on the euro exchange rate for that month
take2 have the same stuff listed for R282, but unfortunately they have no stock (supplier out of stock)
http://www.take2.co.za/games-world-of-warcraft-60-day-pre-paid-game-card-pc-1910414.html
even at that price, it is not worth the hassle to save R5 or R10.
if it is too good to be true, then most likely it is