There isn't really a set amount, it's more mentality and behaviour. This is my take on it.
Whales get the newest toon to 7*/relic in the first 2 days of them dropping. Not worried about the money they spend on the game.
Dolphins; buy toons and packs occasionally but usually have a budget for the month/game.
Guppies/minnows usually only buy something a few times a year, usually a great deal and are very aware of what they spend on the game.
There is also kraken's, which are above whales. They threw money into their fireplaces to boil their kettles just to listen to it whistle. The line between whale and kraken is pretty fine, they both spend unfathomable amounts of money on the game, but kraken just find extra ways to spend money.