I should mention the cost of our app is $0.99. It would cap out at about $2.99. I don't think asking for a dollar a year is unreasonable given the cost of the app.
BTW: Personally, regular payments (especially small ones), do put me off. But I wouldn't mind a prepaid model so much. IE, I pay for a month or six upfront and then pay again to renew. I know this kind of opt-in/out is rarely beneficial to vendors, but in some cases it might work.
There's still an awful lot of the worlds population who earn less than $1 / day.