Hi chip,
that spoiler is different from the one that comes on the standard IS Sport, this one was made for the IS 300, i bought one for my car, as it has a clear brake light fitted in it to.
Cost is around £240 Sprayed, then £40 for the brake light and £30 for the fitting kit (for £280 for spoiler+light, u'd think you'd get a fitting kit, but NO, Xtra) i didn't bother with fitting kit, one of the lads at local garage sorted it out for me..
ooops not forgetting the VAT....