I've three columns; paid 400k, 30m and 48m for them. (not looking for more atm)
Those arch pieces can be all over the map. There's an Atl vendor who likes trying to sell them at 48m; that same one's been offerring a corner piece at 48m for almost 3 months now.

Personally, I've 12 of them, and paid 14m, 10m, 8m (11 times), 6m.
I don't have enough of my project built to know if I need another, tbh, but I'll offer 8m. I'm sure I can find somewhere that could use another door.
Brian