You made a solid choice in getting rid of the PowerBooster. I just did the same to my T-Type this year in June coverting it to the Hydroboost system. You might check G-body parts to compare prices. Also take a look at this link
http://www.powerbrakeservice.net. This is where I got mine but I got the chrome unit, mastercylinder chrome, along with chrome brake lines and spent $1200 for the unit. You can actually do this yourself which will save you a lot of money. If you don't want to do this it just depends on what shop you take your car. Most places charge anywhere $65-85.hr just for shop labor.
Furthermore, there are 4 videos you can watch on YOUTUBE that will show you how to install this system. In the search engine on youtube type the following:
Turbo Buick pt.1 Powermaster to Hydroboost performance brake conversion As stated, just make sure to watch all 4 videos. If you needed help I could send you photos of my set up just in case you ran into problems.
Hope this helps you out. Ride safe out there.
Jamie C.