According to a recent study, very expensive monthly MetroCards are what the future holds. The Straphangers Campaign and Independent Budget Office examined current parrents and projects that fares could cost $3.75 and monthly MetroCards could cost as much as $168. Let that future remain unwritten.
The IBO found that if fares continued to rise at a rate of 8.4 percent, they would jump from $2.50 to $3.75 by 2023, and that's just the base fare. Seven-day fare would increase from $30 to $45, and 40-day passes would go from $112 to $168. That 8.4 percent comes from the IBO extracting the $500 million that the MTA figures to make each year and considering the decrease in riders that will probably come with more expensive fares.
Keep in mind that this is just a "projection" of something that may or may not happen over the next ten years. It isn't gospel.