Javascript Help for Acrobat Form

Javascript Help for Acrobat Form. I have 2 fields. The first is LName, the 2nd is LNameCost. I want the user to enter their name in LName and have LNameCost populate with $249. Any thoughts for rookie?

So far I have in the top of the screen topmostSubform.Page1.LName: :exit: - (Javastript, Client) ------------------------

if (this.rawValue = Don't know what to put here?)

   {

     this.parent.LNamCost.rawValue = "$249";

   }