Excellent advice and instructions there, Spiff. Of course, I'd expect nothing less than that kind of detail and perfection from you!
B-lude, I'd suggest a local paint and body shop. Not a chain or franchise. First, you'd be supporting your local community and you'd probably get a better deal and better work. If you know of any local car clubs, or places where guys with Preludes and other imports hang out, drop in on them and ask around. Heck, you might even find one of them willing to do it for a couple of bucks or a case of beer or something. *(Be careful of letting people you pay in beer, work on your car! LOL)
It's really not that hard and shouldn't cost that much. If you go to the right place and are nice, courteous and sincere, you'll probably get a decent deal.
However, if you don't know how body shops work, they have a book that they go by. It has a "master plan" for how many "hours" something will take to do to every kind of car, specifically. How much time they'd have to spend to remove damaged parts, install and paint new parts, etc. So, you may just get a price quote from them telling you they need X-number of hours to install a spoiler on a 94 Prelude and they'd charge you by that labor cost, paint cost (if applicable) etc.
I would think that it's not a real hard or time consuming task. Mine is factory, and it has two bolts on each side holding it on. Looks pretty easy. I personally could do this to my car if needed, but since I'd be terrified of putting holes in my own car, I'd most likely take it locally and pay someone to do it. That's just me. Good luck!