Louise Worrell, from Croydon, South London claims Woodcote High School staff only revealed plans of the trip four weeks ago.
Ms Worrell fears her daughter Nevaeh, 13, will be left out because the payment needs to be made by February.
She said some parents are forking out their credit cards in a bid to send their kids on the 10-day trip.
She told The Mirror: "If I had longer to pay, I think I could have scraped the cash together - it is really unfair.
"It is really divisive and excludes children from lower-income families – and only the privileged will go.”
Another parent told the newspaper the school asked families for a "voluntary" contribution, but embarrassed children whose parents "chose not to pay".
It comes as Teachers Union NASUWT found that one in six parents weer forced to stop their kids from enjoying a school trip because of costs as high as £3,000.
Chris Keates from NASUWT said: "Access to educational opportunities should not be based on parents’ ability to pay.”
He urged for school to make sure that activities do not exclude large numbers of pupils because they are at "expensive and exotic locations".
Woodcote High School told the newspaper its trips to South Africa had been running since 2008 and provided a range of educational benefits.