It'll probably add another $40 or so. You can probably find a good glasspack for cheap online. I suggest a brand-name like Walker or Vibrant. Mine is a house brand, and after a year and a half, it's starting to wear out. The resonator delete, glasspack addition makes the SVT exhaust a little bit louder, gurglier, and richer but without the obnoxiousness of a straight pipe; IMO, perfect.
Oh and I wouldn't be the first recommending a glasspack over a straight pipe. I know Sujeet (dunno his SN... guy with the boxster) is an 'adamant' supporter of the glasspack, heh.