actually its gona be more than that because its already painted so it will need preping unlike the new ones that come primered
The new one comes with a primer but it still gets sanded, primed again then final sand and top coat. With the good condition painted spoiler, all that's needed is a rub down and colour coat.
As for where I got mine done, Blue one done at Nationwide in Dunfermline when the back end was getting fixed. The Grey one at my old work place, Glenrothes Coachworks, when it was getting the front end fixed. Both charged around the £85 mark.