You'll probably want to get the exhaust to the cats, get as much A/C plumbing (if you plan on running A/C), air intake, cooling fan etc.,etc. The more odds and ends you can get the better.
Don't forget to figure in getting the computer reflashed to get rid of all the OBD2 nonsense.
And as always take the dollar amount you are planning on spending and triple it and you'll be getting close
I would add a few things - you will have the VATS to contend with correct? I know my 95 Cutlass has it. So, if you don't have all the pieces for that (including the steering column ignition lock part) you will have to make/have made a computer to bypass the VATS.
Also - I had an 83 Regal that I put an SBC in. Even with 3.42 gears, I just wasn't happy with the performance or fuel economy, compared to a REAL turbo buick. Just remember that when deciding to go down this road of expenses. Trbo 668 is right - triple your estimates and prepare to pay that. This swap WILL nickel and dime you to death....