CFI sucks money wise. A HUGE amount of time spent at the airport for little money in return.
But it's a step, you make hours and 2 years later you hopefully make it to cargo/commuter where u make $1,500, maybe $2,000 month.
After some times of twin/turbine you can make it to the airline/corporate... start $2,500/month and end up at $20,000 a month at 60 year old with a fat belly and a mustache if you are lucky.
Of course, there are always the lucky ones who are at the right place at the right moment and earn a "shortcut". Aviation is a squeak, you spend a LOT for your training and need to live like a bum for a couple of years before having a reward.
It's not like regular BS, or BA graduates who study 4 years and start to make $$$ as soon as out of school.
I'm pretty lucky, I make $25/h as a CFI, the national average is more like $15/h.