In WWE SmackDown vs RAW 2008 you can earn money by playing normally, but if you want to speed the things up to unlock first the Superstars to buy in the WWE Shop or other content, such as belts, please follow this guide.
Start the 24/7 mode as a Superstar, any difficulty level will be fine.
Choose your Superstar, any wrestler will be fine.
On the calendar select Wrestlemania and confirm that you want to simulate all matches.
Skip all the cutscenes and once the simulation arrives to Wrestlemania save the game and if you want start all over again until you reach the needed money amount.
If you follow this guide to get easy money in WWE SmackDown Vs. RAW 2008 you will earn approximately $ 700,000 or more in about 10 to 15 minutes.