CIS 2016

I suggest considering Moscow, St. Petersburg, and Sochi.
+ We need to find people willing to organize (I think this is the main criterion). Let's say Ive might be able to help with the organization in St. Petersburg, but he would only come as a participant to Moscow. I think Moscow is expensive, while St. Petersburg and Sochi will be roughly the same in terms of cost, considering the ticket and Moscow expenses.

It still depends on where you're coming from.
From the Volga region, it's cheaper to go to Moscow, about 1.5 times more expensive to go to St. Petersburg, and Sochi is the most expensive option.
But the "+" of Sochi is the sea and spring.
The "+" of Moscow is that travel expenses are minimal compared to the other two options, but accommodation is expensive.
St. Petersburg is slightly more expensive than Moscow, but I think accommodation is much cheaper than in the Moscow region.
Indeed, the first question is whether anyone is willing to organize St. Petersburg 2016?