I'd say 150k-250k on average, might get as much as 500k if you advertise and find the right buyer.
The pros you have going for you is...
... its a nice even number. 1k, 5k, 10, 20, 50, 60 all do better selling wise than 5278 diamonds.
... it is one of the more popular stones and its a wedding ring.
The negatives...
... you don't have two the same (least not that I saw mentioned). Those folks looking to use it for in-game weddings generally like the pair to match.
... Those who are wanting it for display can't as most are newbie blessed. So it must be worn to show off. That sounds like a good thing, but in this day and age of so many rare wearables. Those who take the time to squeeze them into their outfit generally treat more expensive=better.
I've had 5k jewelry sitting for weeks on my vendor at 150k on Atlantic (non-luna vendor - Dragonstorm). Not diamond/Not ring, but no movement on it. Multi-gem jewelry, even the lower stones used to do very well. For some reason, they have become slow as molasses.