Select a superstar that is overall better than 90 in attributes (your choice). Begin 24/7 mode and simulate the entire year by going all the way to March on the calendar. Choose the "Wrestlemania" icon. You will be asked if you want to simulate everything until this point. Accept it and answer "Yes".
Choose a superstar that has high popularity and attribute points (for example, HHH or Cena). Start 24/7 Season mode under the Legend difficulty setting. When you get to the locker room, select the calendar and go down until Wrestlemania. Select "Yes I would like to simulate the days" and wait. This will take a bit of time. Participate in your Wrestlemania match and look at your money. It should be in the high thousands, if not millions. Do this two or three times and you will have enough money for everything you need from the shop.