I can help you to find lodging in the Saint-Petersburg. Just now I can offer you two variants:
The first variant is an apartment in the center of the city with the minimum comforts for $25 per day.
The second variant is a flat placed in the center of the city for $70 per day with all conveniences as in the best hotels of the city, but much cheaper.
All additional information you can find at the following web-site: