Can you be paid to taxi an aircraft if you don't have a commercial license?
Yes, as per 61.113:


  (a) Except as provided in paragraphs (b) through (h) of this section,
  no person who holds a private pilot certificate may act as pilot in
  command of an aircraft that is carrying passengers or property for
  compensation or hire; nor may that person, for compensation or hire,
  act as pilot in command of an aircraft.


A person taxiing an aircraft that is not intended for flight is not acting as PIC under this rule, and therefore can not only be a private pilot, but the person doesn't have to be a pilot at all.

There is no specific FAR that qualifies someone to taxi an aircraft, but aircraft operators and maintenance shops train and authorize mechanics to taxi and run-up engines.

Some individual airports have regulations that specify who may taxi and run-up an engine, such as Palm Springs:


  (a)      Only qualified persons shall start and/or operate an Aircraft
  engine at the Airport and/or taxi an Aircraft on the Airport.
  Qualified persons include a pilot, an airframe and power plant
  mechanic, or a qualified technician licensed by the FAA and qualified
  to start or operate the engine(s) and/or taxi that particular type and
  class of Aircraft.


and Whitman County Airport:


  14.20.130 - Who may taxi aircraft.  No person other than a mechanic, pilot, or properly authorized student pilot, certified by the FAA,
  shall taxi aircraft on any part of the airport.