You'd better buy «Podozhnik» card to save money on public transport. This card is sold in metro and costs 50 rub. Just put needed amount of money on it and pay your rides. It will cost you about 10 rub cheaper for a ride, than if you buy a ticket everytime. In the end of your trip you can give this card back at any metro station and return 50 rub. Attention: metro doesn't return amount you put on card, so try to use it all.