If the car means anything to you, spend the money and get a new seat spring frame; you won't regret it. Anything you get in a junkyard will be beat, and the new frame you get is updated, which has more springs to give you more support. The frames you get out of a junkyard will not have the updated frame and will flop around as badly as the seat you have now.

frame - around $155
seat cushion - around $90

Greg
'84 300D, 173k