Personally, I believe that if a person spends no more than $100 a month on gambling is the first sign that he does not have a gambling addiction and is quite able to control their budget. It happens that I spend $200 on gambling but I always split this amount into two different deposits and do not allow myself to spend more than $100 per day.
I truly believe that the amount has nothing to do to determine if a person is already addicted or not. Being addicted is usual but the difference is, there's a thing called responsible and irresponsible addiction. There are gamblers who lose more money than we imagined but despite of it, they are still on themselves.
Regardless of the amount spent in a given period, even how low it is, the addiction will be noticed by the gambler's action outside the gambling world. Like always irritated, skipping work, skipping meals, selling stuff even unnecessary, taking loans, borrowing money from family, close friends, etc.