I'll contribute $2 toward your paint job if only you would put your rear bumper back on
$200-300 for both sounds fair depending how much prep work is needed. You're repainting oem pieces so fitment shouldn't be an issue here, but like KC said earlier, ask for the cash quote since that usually result in a little more discount. Oh, and get them to throw in some extra clear coats for better protection.
To give you an idea, the lowest quote I got was $150 to paint a duck bill spoiler, mind you the spoiler is much smaller size than our side skirt. That's just prep, paint and clear coat, installation costs extra.