Alienation of Affection is not a divorce case; it is its own civil law case. The cost will vary from lawyer to lawyer. There is no upside, but there is a ton of downside when it comes to eroding your spirit, and causing you to relive pain on an on-going basis. You are better off spending your money on shrinks, spas, vacations, etc.
You must file an Appearance, and then you can file your Response and counter-petition at the same time. You must send the Appearance, Response, and Counter-Petition to the other side, but you do not have to "serve" them.
What you are seeking does not exist. You divorced your ex; you did not divorce the lender. The divorce only spells out the rights and obligations between you and your ex, and does not affect the lender's right to collect from either or both of you.