Suspension/chassis, what are you using???
Without a shop rate book;
to change the rear springs, I would guess 4 hours shop rate, or more.
So if they charge $75 per hour, thats $300.
Plus needed parts, such as the ubolts, shock plates, etc.
I ususally figure that on a 42 year old car,
any part that can break, 75% of the time will. Waah.
Do you have spare shock/lower spring plates?
Front spring hangers don't often break, but I would replace the
rear shackles at the same time as the springs.