This is a very easy cheat to pull off, but can only happen once in the game so make sure you have enough to get what you want and anything else.

Head to the Talos District in the Imperial City and track down a house called 'Dorians House', go inside and kill Dorian.
Access his inventory, he should have money, keep pressing 'A' on his money, it will never run out.
Each time you press 'A' your money will go up, but very slowly as he only has 15 gold, so this trick will take time to get a lot of money.

An important note! This trick can only be used once if you kill Dorian, unless you visit his corpse until it disappears regularly.

If you pickpocket him it may be different, but I haven't tested it yet.