Nice site, I dont know much about games but the main consideration here is, where does the game come from? If for example I purchased it would I be able to add new features to the game and build on it for the future without coding skills? or do you need to more about coding?
The reason I ask is that you will get more for it if it can be administered by a non coder type of person.
as it stands I would suggest a price of between $1000 - $1500
It has decent traffic over 650 members, so its worth it.
As with all these things, you can get more from the right person.