Don't know about Subaru's, but back when
I had a pair of Ford Tauruses, the PS pumps
whined for years without failing...

what's exactly the problem with the power steering pump....?
These pumps mostly survive a (Subaru) car-lifetime.
Did you check the oil-level?

A second opinion - or just waiting -  is in order. Whining is typically
caused by cavitation in the fluid and may indicate wear of the pump surfaces
(or even just air entrained in the fluid) but is rarely a harbinger of
failure.

If you need a new pump...
Haven't done Subies, but it is a moderate DIY job in most cars. The fittings
require good wrenches because they are usually ungodly tight. The only thing
to watch out for is that for some vehicles there is a very particular
bleeding process. Not hard, but you need to know what to do. You ought to
find a much more affordable pump with a 30 day warranty (more than enough to
be sure you have a good one) at wrecking yards. At ten model years old the
supply is beginning to peak.

Mike

I would recommend a few things;
Many power steering pumps whine for years.  Determine if this is a
problem for your ears and whether there is any problem with how the car
steers.  As stated above, you might want to just wait, no need to spend
money in advance of a failure when this kind of failure will be
"progressive", not sudden.  Meaning, if it is failing, it will get worse
and worse, but give you plenty of warning by affecting your steering
mildly or getting much louder before it stops working, not suddenly.

If deciding about fixing it;
(A) Find the price of a replacement pump that satisfies your needs whether it
is a rebuilt unit, or a used unit from a junkyard with a guarantee.

(B) If thinking about doing it yourself,
Find out where the pump is on your car visually. Follow the hoses from
the resevoir to the pump and/or look at manuals at parts stores to determine
where the pump is. Get a $15 book from a book or parts store on fixing your model
car or get one off Ebay.  I suggest you see the pump's location with you own
eye's (I don't know for your model ) to help determine if you want to
tackle the job.

(C) Don't be shy, go to your mechanic, or another, and say something like
"that's an expensive repair, is that a rebuilt pump? warranty? (if the labor
is most of the cost, ask ) where is the pump anyway?, can you show me? Is it
a difficult job?"

Try this with more than one mechanic until you are satisfied that you feel you
have enough information to decide what you want to do.

(D) Determine if special tools will be required. Is the resevoir separate from
the pump because the pump is at the bottom of the engine, but easily
accessed once you get under the car? or is it in the middle of the front
of all the engine accessories and will require you to pull the radiator
and most of the front engine accessories to get to it?

As Mike said above, good wrenches will usually be needed, probably
metric sized "line wrenches" which you may not have in your toolbox.

RedCrow

Make sure it isn't the aircon idler pulley
screaming.  I've had to remove, clean and
regrease that pulley on 2 Subarus and one
Datson.