I'm glad you've managed to keep flying through the very lean periods as you describe them. However to accept the rate you've been getting is a classic example of subsidising students and driving down the potential earnings of other instructors. But hey you're on the bus so who cares. And your final comment about good salaries being offered to IR instructors shows that your missing the point. How do you fund those qualifications on an instructors wages?
If you think it's ok to pay professional rates to get professional ratings and then charge half price when you actually work then there really is no hope.