Dragon Ball Z: Budokai Tenkaichi 2 Tips

Easy 1 million Zenny
Fisrt you go to Majin Saga Chapter 11. You should be good buu. Then you fly to the yellow dot in the mountain road (above the red dot). When you fly in you will see Yamcha talk to him and he will challenge you(he is lvl 228). Beat him and you will get 1 million prize money and a equipment slots +4.

TIP: Make sure you power up Buu a little bit because it will be a hard battle.