reclaimed windows in new extension?

Hi all, I'm hoping to hear from building surveyor and glazier next week, but someone here might be able to help in the mean time.

I'm building a new extension and hope I can use reclaimed windows. I have two timber awning windows which suit the house perfectly but they're single glazed and energy report indicates double glazing.

Is it feasible to have a glazier modify the windows to bring them up to standard? Would the cost saving be significant compared to buying new windows?

Theyre 1800 w x 2100 h and 900 w x 2100 h timber awnings.