you will always be able to get BTC just you will get less each time you buy. In January 2017 my girlfriend @unityeagle bought me $50 worth of bitcoin or .05672062 wich is 5,567,062 Satoshi that is worth $932 this year. and right now $50 will buy you .003 or 300,000 satoshi but next year that same $50 will probably only get you .0003 or 30,000 satoshi so forget about the dollar amount and keep your eye on how many satoshi you have.