Is there a legally mandated filing fee and/or deposit in the last instance?

Representation of the People Act, 1976

CHAPTER VII ELECTIONDISPUTES

64. Power of the Tribunal.—TheTribunal shall have all the powers of a civil court trying a suit under theCode of Civil Procedure, 1908, (Act V of 1908), and shall be deemed to be acivil court within the meaning of sections 1[476,] 480 and 482 of the Code ofCriminal Procedure, 1898 (Act V of 1898).

Source:

http://ecp.gov.pk/ElectionLaws/Volume-I.pdf

The Pakistan Supreme Court Rules

PART-II APPELLATE JURISDICTION. ORDER XII. CIVILAPPEALS UNDER ARTICLE 185(2) (d) (e) and (f) OF THE CONSTITUTION.

6. The liability of the parties to pay court-fee in this Court, unless otherwise ordered by this Court, shall not beaffected by any order for consolidation of appeals made by the High Court or bythis Court.

Source:

http://www.supremecourt.gov.pk/web/user_files/File/The_Pakistan_Supreme_Court_Rules.pdf