Extra vendor mounts cost 20 gold (60%) and 200 gold (100%) in the client. Riding training itself has no price in the files; beta players reported about 100 gold in total at 40 and 900 to 960 gold at 60. A Riverglades vendor caps rare crafting materials from 20 gold and sells a 15-day 10% mounted speed buff for 150 gold.
The same week Blizzard said it will take bought gold back and close accounts, and that it has been too lenient.