I thought Valiant Force would release the information sometime soon, but until now i still couldn't find it @_@
So, after months of playing every time I see someone post their screenshot with Prestige information I saved them
Prestige 1- 50 Gems
Prestige 2- 150 Gems
Prestige 3- 300 Gems
Prestige 4- 500 Gems
Prestige 5- 800 Gems
Prestige 6- 1,100 Gems
Prestige 7- 1,500 Gems
Prestige 8- 2,000 Gems
Prestige 9- 3,000 Gems
Prestige 10- 5,000 Gems
Prestige 11- 8,000 Gems
Prestige 12- 12,000 Gems
Prestige 13- 17,000 Gems
Prestige 14- 25,000 Gems
Prestige 15- 35,000 Gems
Do note the number of gems are accumulative.
For example if you have 4,500 Gems you will be at Prestige 9, and will need 3500 more gems (Total 8,000) to reach Prestige 11.
The amount of Prestige are based on gems you purchased, if you buy the first time purchase promotion with double gem you will get double Prestige point.
There are also some bundles without gem that give Prestige point, it will specifically state at the bottom of the pack how much Prestige it gives.
Which Prestige level to aim for? 
Below are the notable reward and good Prestige level to be at.
Mid spender - Prestige 7 - you will get complete 4* set for Healer, Ranger and Guardian
High spender - Prestige 11 - you will get all the above plus complete 5* set for Mage, Shadow and Champion along with 1 x 4-5 stars Arena Hero Ticket
Super Whale - Prestige 15 - you will get all the above plus complete 6* set for Healer, Ranger and Guardian along with another 1x 4-5 stars Arena Hero Ticket and 3x Valiant Ticket
Other additional benefits for each Prestige level can be found in Prestige bonus icon in the game.
(Includes increased bonus energy, free express tickets, increased keys capacity, increased tower effect and many more!)
The rewards will be sent to your game mailbox once you reach the VIP level.
Once a Prestige player, always a Prestige player. The benefits last forever.
