
The guy behind the party is mega-loaded investment guru Charles Brandes -- who throws an annual super expensive Halloween bash at his San Diego estate.
We're told Brandes locked in Aguilera to perform this past Saturday night between 7:30 and 8:30 pm -- at a rate of $16,666 per minute ... plus hair, makeup, travel and other related costs.
Sources connected to the event insist Brandes didn't pay Christina a dime over $500,000 -- but several well-connected sources close to Aguilera are standing firm on the million dollar mark.
Either way ... SICK PAY for 60 minutes of "work."












