The words 'Unlimited Money' can you make your day in real life as well as in Watch Dogs. There is a huge list of things which you can buy if you have enough. Follow these few tricks to get Unlimited Money in Watch Dogs.
To steel cash from civilians, you need to profile them for their bank details, after getting their details, go to an ATM get withdraw the cash. Collect as many details as you can before going to the ATM. To view the bank details check the Statistics Screen.
To collect money like a boss, you first have to buy ATM Hack Boost, Profiler Optimization, and ATM Hack Boost Plus upgrades. These three will help you find the people with competitively more amount of money in their bank accounts. These people will be highlighted as soon as you are in their vicinity. Hack into their phones to gain access to their bank code and ATM details. Do this as more than once and you should be a millionaire.
Another way to get more cash is through "Online Hacking Contract" side missions, you will have to buy the "Online Contract Cash Boost". First login to your Uplay Account from the Main Menu and select Uplay. After you sign in, Uplay Actions will reward Uplay Points. Now you will have the required points for unlocking "Boost the cash payout from all online contracts to get an edge on your enemies" cheat.
You can also draw in cash with the help of "Palace Pack" DLC for which you will have to order the DedSec, Vigilante, Digital Deluxe or GameStop Special Editions of Watch Dogs. It will have the "ATM Hack Boost". It will be given as the Mission Completion Reward, which will help you to increase the cash reward while you hack a bank.
There is always one way or the other in Watch Dogs to achieve what you wish to, if any one of the above scenario does not suit you go for the other. But do multiply your money so that you can complete the missions easily.