2004 Chrysler Concorde Power Steering Rack Leak

I went to garage yesterday for regular maintanance (85K). As the result the mechanic told me that the power steering rack is leaking. Need to replace soon.
The problem is the garage charges too high for replacing this item, which to costly for me.
When I look to online sparepart site, the cost of the power steering rack alone is 1/10 of the garage price. OK if the there will be mechanic fee, but seem not 9/10 of the garage price.

My concern is like the following questions:
1. What other parts that I need to change when replacing these steering rack?
2. Do I need Speed Transmission Proportional Steering item on the Steering Rack for my car? BTW what is the speed transmission proportional steering?

I would like to buy the sparepart online and ask the garage to put it to my car.

thanks