Have a look here:
http://gt-racing.com/products-page/986987-boxster-parts/page/5/
GT-racing has rear wing options under $800, and either their GT3R or early 996 Turbo front bumpers would be easy to add a splitter to. I've got the regular GT3 front bumper...it adds some front downforce, but a splitter would be better. Adding a splitter to this one would be tricky.