Staying alone aint that easy as you thought of... Renting a rooms is ex, moreover also worried whom you stay with etc... If currently because of staying with your family whom is a smokers is a main reason. Why not have a good talk. Then staying outside.. You really need to reconsider..
Be grateful of what you have, even though it is not the best, at least it is something.
you know the children in Africa.... they four five years old have to start to find food for themselves already. some of them by ten years old already a parent, by twenty years old already a grandparent already.
meanwhile, we are almost twenty and still living on our parents. think about how lucky we are. treasure what we have.
don't need worry about cannot re-pay parents. next time with a diploma you can get a job that pays around 2-3k. with degree even higher. surely you can re-pay parents.
there's this saying in Chinese that goes "sky down father mother heart", which means every mother and father in the world love their children.
appreciate what you have.
if you do not like the smell of cigarettes, tell them to quit smoking. anyway, it's also for their own good. I'm sure they will understand and accommodate.
that sucks dude. all the best