Depends how big the car la.. most shops, charge the same, or just very small extra fee for big cars .. ( Not talking huge SUV or Van )
If you have a small car, such as Lotus Elise/Boxster .. then D I Y .. quick and easy,
If you have a bigger car, such as 7 series, A8, S class or Lincoln ... take to detail store la..
To get it done professionally, depends on the condition of the current surface (feel it, if it feels bumpy, then it needs a lot of work), it could vary between $300-$500 per job. Still, it depends on what needs to be done.. but most will involve washing, polishing, and waxing.
I do 3 different wax job a year:
Big - clay bar, fine sanding on scratched area and rubbing compound, then polish, cleaner wax, then carnuba wax, then seal. This job takes anywhere between 8-12 hours with my 3" multi-speed polisher.
Med - clay bar, wax and seal. Takes about 6 hours
Small - clay bar and seal. Takes about 4 hours.
If sealed propely, polishing should not be done too regularly as you are just removing the outer layer wax and re-apply it, and seal it again.
If you've never done any waxing before, you can start from scratch by using dish washing liquid to wash your car (lots of it). It will wash out any wax, smock, oil from the surface and you must apply some wax otherwise your car will be naked!