Once again I would like to highlight the importance of only giving instructing a go if you really think you are suited and happy with the idea of teaching. The students out there need competent, cheerful instructors who put effort into their work.
Having said that, if you do manage to get an instructor's rating first and get work as an instructor you will then be able to claim the expense of your IR when tax time comes. You MUST be working as a pilot though before you can claim training related expenses such as an IR. You could be surprised at how much you can get back in your tax return
