I played during the $2.00/hour days. It is very easy in an hourly billing system to run beyond what you budgeted. All it takes is one good night when you're flying Sierra Hotel sorties and you don't want to quit.
Keep it simple. Fifteen dollars a month is easy to budget. You know exactly how much they're going to charge you and what day it's taken out.
If your budget is so tight that fifteen dollars is too much, cancel for a while. No shame in that. I just came off a whole year without online access because money was tight and AH is lower in priorities than rent, electricity, gas, water, and school lunches.