Dealers will always rip you off...dealer = last resort. Mega expensive!
First, when you say your wheel shakes, do you mean steering wheel or tire/rim vibration?
1) I would investigate the leak/wheel shake more before replacing the entire rack. I have not heard of the rack leaking causing a vibration...I'm no expert though...it could be the rack, but I would do some more testing first...IE check tire wear, rotate tires, maybe get an alignment since you know it's out...check your brakes...worn pads or stuck caliper pistons can cause funny vibrations. My initial guess is that the wheel shaking is independent of the PS fluid leak.
2) If you have a sizeable PS fluid leak, you WILL get the high pitched whining/squeal/groan/creak sounds once the fluid gets low enough...that's the sound of the pump trying to pump when there isn't enough fluid. If your leak is not leaving puddles on the ground, and you don't have squeal yet, I would wait it out some while investigating.
3) Most people I have heard from have PS fluid leaks from hoses...the raw metal mechanical parts rarely just...fail. It is the rubber o-rings, gaskets, seals, etc that are the weakest link and will cause a leak. Meaning, you can rebuild your rack yourself, buy a rebuilt unit or a used unit from ebay, or use some power steering stop leak and see if that fixes the leak.
For reference, my Nissan Xterra power steering gear was $1800 just for the part from the dealer...brand new complete gear case. Crazy. Rebuilt unit from NAPA was ~$300...a rebuild kit with the seals/gaskets to rebuild your current gear was ~$45...Lucas power steering stop leak was ~$5.
I started with Lucas PS stop leak from Wal mart, and never did anything else. Not a "root cause" fix, but for $1795 I will accept it.
My 318ti, like I said, leaked at the hose. I Cut about 1/2" off the end of the hose, got a new clamp, and re seated on the reservoir...and refilled with stop leak. Problem solved.
Anyway, like I said, I am no expert at steering racks, but before I replaced the whole thing, I would try a few other things first
Probably what I would do, is just keep driving it while rotating tires, checking brakes, etc. Check the fluid level occasionally. Once it gets kind of low...or when it makes a squealing sound, just top it off with Lucas PS Stop Leak. it is designed to be mixed with your current fluid like that-no draining needed. Ideally, it is a long term kind of process...top off with stop leak...drive a while...check fluid levels...top off some more, and don't add cumulatively more than 2 of the bottles...if it's still leaking then you need a rebuild.