NEW YORK (TheStreet) -- Republican presidential hopefuls will get their chance to seek the support of billionaire brothers Charles and David Koch as well as hundreds of other wealthy conservatives at an event that kicks off Saturday in California.

The event will be hosted by the Freedom Partners Chamber of Commerce, a group affiliated with the Koch brothers, whose network alone is expected to spend almost $1 billion on the 2016 election. The three-day conference is expected to draw 450 of the biggest backers of the Republican party, including representatives of casino mogul Sheldon Adelson and hedge-fund manager Paul Singer, according to a report by Politico.

Former Florida Governor Jeb Bush, Texas Senator Ted Cruz, Wisconsin Governor Scott Walker, Florida Senator Marco Rubio and former Hewlett-Packard(HPQ) - Get Report CEO Carly Fiorina are all expected to attend, Politico said, but not Senator Rand Paul of Kentucky.

So far, Right to Rise, the super-Political Action Committee backing Jeb Bush, reported raising $103 million in the first half of the year, far more than the super-PACs of his rivals. Cruz's super-PAC Keep the Promise has raised about $38 million, and Walker's Unintimidated PAC has raised more than $26 million. Rubio's Conservative Solutions PAC reported raising more than $16 million since early April.

According to Politico, the Koch brothers are not expected to formally financially back any individual candidate in the Republican primary, although Charles Koch has said about one-third of the $889 million in planned spending will go toward state and federal elections. The remainder of the spending will reportedly go toward universities and public-policy advocacy groups.