Actualy in reality The group who owns Man City (ADUG) own arround £550BN. The £60BN you mention is Sheikh Mansour perosnal fortune. However even those figures aren't anywhere near the true wealth behind City. City were bought for one reason. As a huge marketing tool for Abu Dhabi. The true financial wealth behind City uns into the Trillions.
On topic however. Like the chap with the Jar Jar Binks Avatar says it's too boring playing as City. Having lots of money to throw around and a squad of superstars is no fun at all. Be a man and start as Hyde United.
Ofcourse it all depends on what you set as your season expectations. Be conservative and the board will give about £40M, However tell them you can win the league and they will give about £80M with a wage budget of around £300,000. However this is all irrelevant as every now and then the Chairman will come along and give you another £40M or so to spend just for fun so i think it's probably impossible to run out of cash.