What is the cost of a play station

There are a lot of factors that have to go into this.
A) Which console? You didn't really specify a console. It sounds like you're asking about an original Playstation.

B) Where you get it from

Just looking on Amazon, these are the prices I found:

Playstation 1: $17.95 used
Playstation 2: $40.00 used
Playstation 3: $144.95 used / $189.99 new
Playstation 4: $319.99 used / $399.99 new

Of course these prices are subject to change depending on when and where you get them.