Hello,welcome to Ukraine!
About food.This depends on your preferences.I'd advise you to have one hundred hryvnias per day,it's around 13 USD.Though it's quite possible to eat here having 50 hryvnias.But you have to take into account individualities of different places.For example,in Kiev I'd rather have not less than 200-300 hryvnias per day,here,in Dnipropetrovsk,100 would be enough.(I didn't mean restaurants and cafes in this text lol)
About the bus pass.I don't think you can get a bus pass here.You just have to pay fare every time you get on the bus.In Dnipropetrovsk a ticket costs 3 hryvnias,around 0,40 USD.In Kiev it may be two times more.
About the accomodation.I've been living here all my life and I've never known a Host family.But I'm not sure this kind of travelling doesn't exist here.To rent a flat in Dnipropetrovsk costs about 3300-4000 hryvnias per month,i.e. 400-500 USD (just like in Berlin!..haha)A room-around 50 hryvnias per day,i.e. 210 dollars per month.
Activities.I'd say this item also depends on which city you'll live in.And to speak sincerely,I know that here if you have not very much of money your activies are going to hover somewhere above zero,if you have enough of that stuff,you won't be able to make out if it's Western Europe or what lol But I'd advise to have not less than 100 hryvnias (13 USD) per day.
So I think it'd be enough to have 6000-8000 USD for the term you're going to spend here.
From my own experience I could say that usually foreigners are surprised to know about our prices,always say it's cheap.In general they like it here.
Wish you good luck!