On my "main", or at least the char i use to play the gtn game, i sit on around 150-200 mill most of the time.. I had some crazy spendings, which put me down to around 140mill, and then i bought about 20 hypercrates on gtn, so atm i got around 40 mill on that char.. Give it a week or two, that will go back up to somewhere between 180-200 mill again, when i sell all the hypercrates for a fair profit.
On the rest of my chars that i play, i just send over a couple of mills every time i need it..