It’s a hard question to answer without knowing more details.
It’s going to depend on:
+ How much electricity costs where you are
+ How big your piece is
+ What temperature (cone) you’re going to fire your piece at
+ What kind of kiln the studio will let you use (if you can find one who will let you use it)
+ How much they want to charge for this.
You’re going to need to rent the whole kiln for the firing, since it’s unlikely that they will fire other pieces in there, especially if you didn’t get your clay from them.
If you’re near Philly, The Ceramic Shop charges between $25-75 / firing.