CIS 2016

I'd venture to suggest that renting a base/mansion in the Moscow suburbs/near St. Petersburg or Sochi would cost approximately the same.

I'm a bit doubtful. In May, it's not yet peak season in Sochi, and there are plenty of available spaces, so bargaining is possible. For the sake of attracting a crowd of 30-50 customers, many owners might be willing to make significant concessions – both in price and terms.