Prices seem to vary throughout the day though e.g. last Sunday I got 1.6m for VOs in the morning and only half that in the afternoon at the same station.
All prices are dependent on BGS states of the station owner - though this is most obvious with the really expensive gems, of course.
Void Opal prices are doubled by each of
- Investment
- Civil Liberty
- Pirate Attack
States are updated at about 1pm UTC each day at the moment, so that adds on a lot. Pirate Attack is - after a bit of a "startup" rush after 3.3's release - a relatively rare state.
(Most likely the Pirate Attack ended between the morning and the afternoon)
Low Temperature Diamonds, on the other hand, have their price increased by
- Investment
- Civil Liberty
- Expansion
This is a fairly common combination to see in player-supported systems, so it's much easier to find a system with all three of these, which beats the price of Void Opals at a system which only has two of that gem's preferred states.