Well, for starters, this doesn't say anywhere that the Saudi government supports ISIS. I keep seeing variations of this reiterated mostly by western political analysts but this only goes to represent to their ignorance of middle-eastern geopolitics, as a matter of fact, if anybody knows two shits about the middle-east, he/she wouldn't say something like that. To clarify, ISIS is in itself a threat to most forces that are currently in power in the middle-east. By ideology, ISIS considers most arabic governments to be infidels "Kuffar" and allies of the west "Dar al Harb".

Regarding private contributors, this is undoubtedly true but as clarified in the linked article, it's not the large sum currently. Why are there private contributors you ask? Because morons "Sunni" governments fund morons -like ISIS- to fight other morons "Shia" governmets e.g. Iran which in its own right funds some morons -Hezbollah and its ilk- to fight the original morons, in dreams of having a moronic sectarian consolidated power dream.

[Edit]: I originally put the phrases "Sunni" and "Shia" in quotes because they're usually misrepresented by non-muslims. There are different branches of Shia and different branches of Sunna "Sunni". There are newer terms like Wahabism and Ahmadiyya. Each of these terms can be interpreted in a number of ways, the "academic" distinction is quite clear but the reality is quite complicated -in short, several groups, members with different ideologies claim one of the aforementioned terms to be the one that identifies them and that they fit the most accurate description of that term-. Note that this is a gross oversimplification.