Check http://tinyurl.com/3eb77 (Number 330-145 from
http://www.partsexpress.com) I have put one of these in an '96 Accord
and in an '87 VW GTi. It is a great unit, it is only $40, and the on
board relays can be configured to work with almost any power door lock
system.

The Accord installation was almost trivial, as the car had power door
locks already. The VW took a little more effort, as it had central
locking with no actuator in the driver's door. (I found an actuator at
the junk yard and put it in the driver's door. Vacuum tubing, if needed,
can be had from the dealer or from http://www.mcmaster.com, part number
5239K11).

The remote lock unit referenced above comes with a number of fairly
generic wiring diagrams. It includes diagrams for bi-pressure systems
like in the VW (and probably your Audi), except that those diagrams did
not apply to my car. Also, the system can be programmed to give lock /
unlock pulses up to 30 seconds for bi-pressure systems. Again, this was
not necessary. The regular .8 second pulses work just fine.