Tough to find. Occasionally someone on this site lists them for sale. I wouldn't be surprised to pay a couple grand for everything.
I used to be indecisive. Now I'm not sure. I feel like I am diagonally parked in a parallel universe. 1968 400 convertible (Scarlet) 1976 T/A - 455 LE (No Burt) 1976 T/A New baby, starting full restoration. 1968 350 - 4 speed 'vert - 400 clone (the Beast!) 1968 350 convertible - Wife's car now- 400 clone (Aleutian Blue) (Blue Angel) 2008 Durango - DD 2008 GXP - New one from NH is AWESOME! 2017 Durango Citadel - Modern is nice! HEMI is amazing! 1998 Silverado Z71 - Father-daughter project 1968 400 coupe - R/A clone (Blue Pearl) (sold) 1967 326 convertible - Sold 1980 T/A SE Bandit - Sold
I recently purchased all the various pieces to redo my 68s AC system. It can get expensive and it's very time consuming looking for the factory correct parts. There's some common things between the 67s and 69s birds, but a lot is specific to the first gen bird's. If you're open to a system that looks close, it may be easier to find a full Camaro system. I saw most of the parts from a 68 Camaro on ePay the other day for around $500.
The correct 68 bird, exhaust muffler, POA valve and a few other things are very tough find. I'd say to get everything you'll probably spend $2,000 or so, if you want correct. It took me almost a year to find what I needed.
1968 Pontiac Firebird 400 Convertible - April Gold/Deluxe Black Automatic 1968 Pontiac Firebird 400 Coupe - Aegena Blue/Standard Teal 4 speed 1968 Pontiac Firebird 400 H.O. Convertible - Alpine Blue/Deluxe Teal Automatic 1968 Pontiac Firebird 400 Coupe - Autumn Bronze/Deluxe White 4 speed