Edd,
You will get paid a certain amount of 'Allowances' when you're downroute, but they vary wildly, depending who you work for, and whether you are longhaul or shorthaul, and which destination you visit.
E.g. In our company, you could go to Harare on a 5 day trip and get paid £375 for it, or do a 3 day Denver and get paid about £40 more for it!
Some airlines will pay an hourly rate for every hour away from base.
As you can see, there a lot of variables, so have a look at what the different airlines offer.
Hope this helps.