NOS springs if you can find them run $800-1000.
A set of original take offs - removed in the first 5 years or so - in survivor condition could be worth $600-800
Original re-arched springs are $450-550 last I saw some.
A set of original springs removed during a restoration and needing refinishing will ALSO NEED RE-ARCHING(100-120)
So maybe $300-350 as is for unpitted original springs delivered to the customer.
Just make sure when you rebuild them to buy the spring end sliders from EATON - because they have to correct ones for the rectangular "bun" pockets.
I paid $125 for a 4 leaf set which were really nice other than being through an accident there were a couple bent leaves and a spring eye nearly wrapped under. The shorter leaves, which I was after were fine to replace some of my own which were excessively pitted.