First have a saved game that has a good amount of money. go to 2 player and open the same file that your player 1 is on. go to the first track(the shortest) and raise the bet to the max. the more money you have, the greater the max. run around the track with the player 1, while the player 2 just sits there when u complete the track, #1 will get the $. when #2 gets too low, save #1, and exit to the #2 load screen. reload the #2 on the #1 file. do this again and again. eventually the max bet will top out at 9999, but keep doing that. you will have $ in no time.
Go to either Bazkuan Ski Course, Wacais Beachside, Dyna Mountain, or Bomber Coaster Lake and drop down to the waterfall, water, mine etc 14 times. Your bank will be soon filled with more than 5 million dollars and you will get to enter the Bomber Castle of Mirror Mode whilst you get top from everything!