Not to try and piss you off or anything but hiring a pro might not be all that helpful to you. 95% of the pro detailers out there are going to use a rotary and using that takes a completely different technique than with a PC. If you still want to to hire someone, and have them use a PC (they might upcharge because of the extra time it takes) the total cost is really going to depend on how bad the car is. It could be anywhere from one hundred something and up for a proper detail.
Some polishes dust alot. That's just something that your going to have to deal with or switch to a lower dusting polish. Spraying the area with a
50/50 mix of isopropyl alcohol and wiping with a towel will quickly remove any polish on the paint. For the plastic pieces try something like PB trim restorer.