LA Porsche Dismantlers is a popular place for salvage body parts:
http://www.911pcar.com/
Here is their online listing for 97-04 986 BOXSTER body parts to give you an idea of the prices:
Boxster S front bumper cover $400 used or $550 new
Boxster S bumper assembly $900 used or $1200 new
97-02 bumper front cover $350 used or $500 new
97-02 bumper front assembly $900 used or $1000 new
03-04 bumper front cover $450 used or $550 new
03-04 bumper front assembly $900 used or $1000 new
bumper front aero $1000 new
bumper rear cover $350 used or $500 new
bumper rear assembly $900 used or $1000 new
door mirrors $200 each
97-02 rear deck lid/spoiler assembly $200
03-04 rear deck lid/spoiler assembly $300
door assembly $6000-1000
front fender $250 used or 350 new
hood $400
1/4 quarter panel $700 w/innerstructure & rocker
aero rocker $400 pair used
door handle $200
front body assembly / front clips $4000-8000