In chapter 1 of Moonraker James Bond is in his office ploughing through a mound of paperwork. Fleming tells us a little about Bond’s routine while in London between assignments. He also tells us his income:
He earned £1500 a year, the salary of a Principal Officer in the Civil Service, and he had a thousand a year free of tax of his own.
What we learn from that is that 007 has a total pre-tax income of £2,500. Although not stated, the thousand a year are presumably his inheritance in the form of a trust fund.
When he was on a job he could spend as much as he liked, so for the other months of the year he could live very well on his £2000 a year net.
So he also relies heavily on his expenses. He regularly plays cards, so presumably tops up his income with that.
Although £2,500 doesn’t sound like very much, remember that Moonraker was published in 1955. Adjusted for inflation to that is the equivalent of £63,000 in 2017. £37,800 is his civil service salary and £25,200 his private income.
In US dollar terms 007 was earning the equivalent of $7,000 before taxes in 1955. Today £63,000 currently converts to around $81,000.