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I decided to put in some effort and provide some statistics because a lot has been said about weather conditions and prices, but there hasn't been any concise analysis yet:
1. Weather.
The comparison is based on weather observations and statistics from gismeteo.ru:
May 2014:

May 2015:

May 2016:

As you can see, no one here freezes, and there are no extreme sub-zero temperatures. To make it clear, almost everyone changes their tires around mid-April at the latest.
Further, when considering the total cost, we get an interesting picture. No one has compiled summary analytics for the cheapest accommodation option, but here it is:
Yekaterinburg: Accommodation (breakfast included) + Meals (lunch, dinner) + conference room fee + tournament participation:
900*7=6300; 900*7=6300; 1000; 3000;
Total: 16600 rubles.
Volgograd: Accommodation (breakfast included) + Meals (lunch, dinner) + conference room fee + banquet + tournament participation:
9600; 700*7=4900; 3500; 2500; 3000;
Total: 23500 rubles.
These figures were collected based on a full board basis and presented for general understanding.