It depends on the time of year. The Astoria and Kempenski are nice, but a little off Nevsky Prospect. The Grand Hotel Europe, Raddison SAS and the old Sheraton Palace (private now with another name) are on Nevsky Prospect and put you at tourist HQ central. There are some others that are not so pricey, but not 5 star. I use to stay at the Pulkovskaya and the Pribaltiskaya ofeten in the past. The former is toward the airport and has a Metro nearby, the latter is on the Baltic Sea, but you need to take a bus or taxi to the nearest Metro Station - Primorskaya. Hotels and transport are your biggest expense items. Go to the non-tourist traps so you won't get ripped off. A good sign of a tourist trap is those areas where you see a lot of foreigners, many small booths set up in tents and they take credit cards!

Just search the web for any deals - you'll be lucky to find them. Also, the new Novotel is very nice and is located about 3 blocks from the Moscow train station. The Metro stops of Mayakovskaya and Ploschad Vosstaniya are nearby. The Novotel is located on Ulitsa Mayakovskogo about 100 meters off Nevsky just down from the KFC.