When you find the location of the lost hoard of the obelisks, the treasure includes 250,000 gold. Open and close the location or chest it's at before leaving the location and the gold will increase by 250,000 gold pieces every time. Repeat until you have 9,999,999 gold pieces.

NOTE: This trick relies on a bug in version 1.0. It will not work in version 1.1 or later.