Firstly, if you're talking airlines, forget Captain pay. You'll need to do time as an FO first.
FO pay: Well, that probably varies between APPROXIMATELY £25,000 in a turboprop as a start salary, to £40,000 as a BA FO for starters.
Whatever way you look at it, the investment is massive and the risk even more so that you may never land a job.
Can you add up and talk sh1t? If so, get a job in the City and save your bonuses. Then, and only then, go do it.