Perecles introduced the idea of a "theoric fund" to pay for poor people to attend the theatre, thereby making theatre open to all classes. this happened around 450 B.C.E.
The Theoric Fund was the name for the treasury that handled the financial dues for all the festivals, sacrifices and public entertainment of all kinds, as well as the distribution of money to those who could not afford it in terms of the generosity of the state. It was established so that the lower class of Athens could afford to go to the public festivals of worship. Most of the money came from the public treasury though a select few individuals would also donate and take some of the burden of funding upon themselves.
Originally there was no charge for the festivals and the audience would often degenerate into fights due to the lack of seating. Because these outbreaks became so commonplace, an admission fee was instituted, to cut down on the violence. This, however, did prevent a portion of the population from attending the festivals.
The Theoric fund was established soon after. A citizen would recieve something akin to a voucher, one for each day of the three day festival of Dionysus.
in the late forth century B.C.E. the cost of admission was standardized to a cost of two obols.