I already have plenty of in game money and there unfortunately no. However, races and missions will help you to gain ranks fairly quickly, you gain more RP quickly by doing missions with crew members. So if you are in a crew then it would be best to do missions, sports such as tennis etc.

There are some lobbies where you can rank up a ridiculous amount, up to level 1000 I believe. However there may be a punishment for cheating (modding) so I do not advise that ..

If you are not in a crew maybe create one with some friends and play the game together, as I said before doing things on the game involving crew members will gain you more rep than doing something normally or with friends.