Here is an example on what ATP say on their website:
ATP flight instructors receive a very modest base retainer fee, plus additional flight-hour pay and bonuses that correspond to students' on-time, first-time checkride pass. Instructors can earn between $1,800 and $3,000 per month.
At the ATP Scheduling Center and Instructor Proficiency Program in Jacksonville, FL:
$1,500 per Month Retainer
FREE Housing
While at your assigned Training Center:
$750-$1000 per Month Retainer (varies by training center), PLUS
$100 On-Time, First-Time Checkride Pass Bonus for each student, PLUS
$7.50-$12.50 per Flight & FTD Hour (varies by program), PLUS
$15 per FAA Exam Proctored
Housing Available at Training Centers
for $300 per Month (furnished, no lease required)
So i guess is try to get the commercial, then CFI, II and MEI and starting working for a school and make your dues. I was hitting 80-100 hours a month wen i was teaching and i was earning 20$/hour.
I know a few guys that was working really hard and hitting the max they could, 8 hours a day 7 days a week, that is 224 hours a month (of course subtract a few for cancelations, maintenance, weather etc...) but your could be doing really good
and get your 1500 hours in just 1 year. The biggest problem that i see is hitting the 500XC not the TT, but then again ATP XC is different so always take your students to different airports.