A full drain and refill would probably be about $100 - closer to $200 if it is flushed out because it was getting rather dirty. Your owner's manual should show the recommended replacement interval - probably same as for brake fluid. Neither are newar as critical to renew periodically as lubricants like engine oil, transmission fluid, and at typically much greater intervals - differential and transfer case oil and wheel bearing grease. Many people never change brake or power steering fluid unless they notice a problem with that function - not a good idea, but also not likely to cause a problem if it goes 80-100,000 miles without a change.
Personally, unless you are trying to scrupulously follow the maintenance manual to preserve your wrranty coverage, I would not worry about it as long as it is the normal slightly yellow color and basically transparent, though oily looking. IF it has dark streaking in the fluid, or certainly if it is blackening, then I would change it. Can go to a mechanic for that, who should unhook hydraulic hose from the power steeing pump AND from the steering gear, drain, fill, and deair the system.
For do it yourself, you will go a lot of the way by using a large basting syringe to remove all the fluid you can from the reservoir, then refill with specified fluid - preferably the manufacturer's brand to avoid mixing brands. Will cost maybe $5 more for the quart or so you will need to use manufacturer's brand and of course you have to go to their parts department to get it usually, but not a good idea to mix brands, particularly as they have different base chemicals and different boiling temperatures and additives. That will replace probably a bit more than half the fluid in the system and clean it up a good bit. Of course, if actually blackish rather than just faintly discolored, then something is going on that should looked at by a mechanic - dirt getting into the system, oil getting too hot in the pump, or some such.
