Its specialist work- i doubt you will find pricing on the internet for that reason. Can they be repaired rather than replaced? You will need to get some craftsmen out to quote as its so specific but I woud advocate repair in the first instance- I've seen really good repairs to similar windows that were in very poor condition. Where are you op? Some local councils have a craft skills register for craftsmen. Good luck!
As SausageDog says, talking to the local conservation officer might be a good start.
Costs would depend on the number of windows, the cost of the materials, the time needed to repair / replace, etc.
I'm imagining you've got 15 windows and I'm going to cheerily estimate £5000 + VAT, based solely on how much entirely different things cost to repair / replace around our house. That's entirely random, mind you.
Thanks so much for the replies. We have identified some that can hopefully be repaired, but some had UPVC put in without consent in the 1970s. The Heritage bods are strongly suggesting replacements in return for permission to extend. I didn't think of asking them for suggested craftsmen, but will do.