I had the same problem / choice a few years ago now. I was making great money doing what I was doing (at least 2.5 times what I am now!!).
Finally it came down to a choice of either fullfilling a life long ambition, or deciding to settle for second best, yet still be relatively financially secure. In the end it came down to thinking if I don't go for it then I'll always know I settled for second best. I'd rather give it a go and at the end of the day be happy that if it didn't work out then I'd tried, and / or live out doing something I love.
Money isn't so good - but if that's your motivation you're in the wrong game!
Your predicament is why I dislike flying schools so much. YOU are the paying customer! YOU tell them when you can fly and train and get THEM to work around YOU!! This seems to be the only industry where you pay upwards of $180 per hour to be treated like cr#p. Too many people fail to remember the old supply and demand thing. There are so many instructors desperate for hours who will fly around your schedule - they have no choice, for any number of reasons.....
Name another profession where you offer to pay (min) $35K+ and and they tell you when they will give you the priviledge of taking your money. YOU are in charge! Shop around till you find someone willing to provide the service you need. Don't be suckered into being sold "The Dream", ie: "Train with us, get an instructor's rating, instruct for free for 6 months and Qantas will be begging to employ you...". Heard it all too often.
Never work for free. You paid and worked too hard for it all.
One last thing - for an instructor's rating if you can find another "training buddy" then you will reduce your training costs. Instead of paying for an instructor to play the passive "student" role, you will have a training partner to do it for free, and vice versa. Not sure about the exact details, but look into it.
I have never regretted my choice. Job satisfaction is everything. A lot of polotics and rubbish to put up with, but find a job where that doesn't happen.
Good luck with your choice!