We can give the OP (tembusu92) our same opinions about pricing privately. I messaged tembusu92 to say that I am happy to discuss prices privately. Other forum members who are familiar with the secondary market can message him as well. We just don't want to use this public forum to get into discussing preowned prices on specific pieces. That WPS rule against discussing street prices serves a useful purpose that I have come to appreciate from visiting other forums.
Other considerations are condition (overpolished?), full set, service history, and condition of anti-reflective coating (1815 Moonphases in particular have had problems with that).