In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
According Dan’s info about efficiency of steam system conversion into two-pipe vapor Paul system from (“The lost art of steam heating”, 16th print, pp. 249 -251):
"Long absent, soon forgotten" solution on average saved 35% of fuel and paid off within first heating season.
This was a good way for steam systems retrofits. Does anybody has experience with Paul system? What’s the vacuum operating range? I would appreciate greatly more