The prices will certainly not be like in St. Petersburg, especially considering that some international resorts have been closed, so there will naturally be more demand in Sochi. But you can also stay not in the city itself, but in the suburbs, for example, in Lazarevskoye. The coastline is the same, the sea is the same, and it takes only half an hour by minibus to get to Sochi. We weren't planning to stay in the very center of St. Petersburg anyway.