Can I substitute a different type of flour and still achieve similar results? I have so many flours, I am hesitant to buy more :)

Chapati flour is just very finely milled whole wheat flour, when you come down to it. If you have a white whole wheat flour in amongst the stash of flours, it will work just as well. If it came to it, you could probably give regular whole wheat flour a few pulses in a food processor to reduce the bran particles a bit more and use that. You could also do a mix of the whole wheat and all purpose flour- I'd say maybe 3/4 cup whole wheat and 1/4 cup all purpose for each cup of chapati flour.