The correct order is:
FAA medical
Private Pilot
Instrument Rating
Commercial pilot
Certified flight instructor or pipeline flying (or something similar for low time pilots)
ATP
1500 flying hours are required for an ATP (airline transport pilot cert). AND unless you are lucky enough to get a job with a commercial cert at about 250 hours, you may have to pay for all of those hours.
Take out your calculator and multiply 1500 times 150...let me know what that costs you.
I know only one guy paying for his time to build up 1500. Most guys I know are instructing. Most instructor jobs don't pay we'll, but where I work the pay is decent. Some months, it is possible to clear $5000 pretax. I also know a few guys who got hired to do pipeline flying in Texas with as little as 250 hours.