I was feeling brave and sprayed all the plastics on my Fiesta ST 2 days before Ford Fair.
They're pretty easy to get off; you just need a thin flat bladed screwdriver, and a little bit of courage. The worst bit to get off is the lower rear valance, as the shitty rawl plug type screw things (no idea of the correct name for them) are unusable once you've got them off.
You can do them yourself if you're confident, and have the time to sand, primer, spray, smooth and lacquer them. I cheated and used plastidip, so although they're not shiny, they're not that dull standard grey. I don't know how durable the paint is going to be, only time will tell.
I don't know how much it'd be if you want it done professionally, a couple hundred maybe. You're best off getting some quotes.