CPL= Commercial Pilot's Licence
ATPL= Air Transport Pilot's licence (I think!)
CPL allows you to earn money from flying. e.g.: air charter, flying instructor (if you get an FI rating). If you want to work for the airlines, you need an ATPL. This is basically a CPL with an IR (instrument rating) and passes in the ATPL ground subjects. To get a CPL, you need 150 hours; for an ATPL you need to be 21 and have 1500 hours. Until you have 1500 hours, you have a 'frozen ATPL'. With this, you can't fly for an airline as you don't have the hours, but you can get some other sort of flying job.
In this country, an ATPL integrated (full time, 1 year approx.) course costs about £50-60,000, or you can do a modular course, spread over perhaps two years, which will cost £30-45,000. You do this in modules. ie.: PPL (Private Pilot's Licence), then do some hourbuilding, then do CPL, then a multi engine IR and the ATPL groundschool.
You can do this in other countries as well (e.g.: USA, South Africa, Australia (where I want to do it)), and it could cost a third to half of the price.
If you want some web addresses of schools to look at, e-mail me. I've had information from about 45 schools so far; expecting more any day!
Have a look at websites like
www.avasp.com and airline websites for more info. The British Airways website is quite helpful, too.
www.britishairwaysjobs.com.
Hope this helps!