As you say it does depend on a lot of things like rostering etc. If you were to have an average month of East Coast flights you would be getting about £370 (depending on the exchange rate), assuming you'd be doing 5 flights in that time. If you have a really good month it can be a lot more than that, say with a caribbean or a far east trip.
I enjoy the social life so it's quite difficult to save the allowances, as the lure of shopping and drink can be too strong. I have to be reminded that we get real money, not green shopping vouchers....(usually by my boyfriend). I hope that's some help, although there are no guarantees.