Life is quite expensive in Russia. And in addition, because of the boycotts imposed by Putin, and some shortages due to the war with the Ukraine, it's difficult to estimate the current situation.
First, if you want to be well prepared for your trip to Russia then you should take a good amount of cash with you, (Euros is best but sterling is accepted), unless your bank card has a low commission rate. In Russia every town, whether it's as big as St Petersburg or hiding on the Kamtchatka Peninsula, has a bureau de change. But if you are going to stay in a village then remember to get some roubles first! In the same way, the commission is lower for changing money in a bank or bureau de change rather than in a hotel or airport.
The exchange rate varies but on 10th March 2015 it was RUB 65.30 to the euro, or RUB 92.59 to the pound. When it's at this rate then more or less everything seems accessible. Actually, life is quite expensive there. For a two week stay in Russia you should allow a relatively large budget (at least £500), especially if you are staying in Moscow or St Petersburg.
In Russia it's easy to eat as much as you want, of good food, at fairly good prices. There's nothing better than going to the stolovayas (cafeterias for students or workers) where you can eat typically Russian dishes for about RUB 316 (£3.25) each.
If you are going to cook your own food then obviously you should use local products from the markets. In the supermarkets the prices are more or less the same as at home. If you want fresh fruit and vegetables then it's better to buy them from the babushkas selling their garden produce in the street.
When it comes to restaurants, you will be disappointed, even if you have a high budget. Even if you do get something delicious, there's not much of it. And the prices are quite high for so little food. You need to budget at least RUB 760 (£7.80) for a mini-plate of 4 pelmenis- Russian ravioli. You'll leave the restaurant with your purse much lighter but your stomach still empty!
In the same way, if you are thirsty and you want to buy water (because you are strongly advised not to drink the tap water) then it is expensive (it's almost £1 for a small bottle). It's cheaper to change your habits and try some Russian thirst quenching drinks that aren't expensive like kvass (made from fermented bread) or mors (made from red berries).
Hotels in Russia can be quite expensive, especially in Moscow and Saint Petersburg. Youth hostels cost a minimum of RUB 635 (£6.50) for a place in a 10 bed dormitory, whereas for a hotel you need to allow between RUB 952 (£9.50) and RUB 4,442 (£45.75) a night. For £9.50 you would get a room with a sink in it. The shower and toilet would be in the corridor.
If you want to stay in a village (especially one of those that is "used" to tourists, like on the shores of Lake Baikal) then you can stay with a local for about RUB 635RUB (£6.50) a night.
Transport is really cheap in this country. For a trip in town you only need a few pence. As to the train, despite the enormous distances you travel across Russia, the tickets are a lot less expensive than ones you buy in the UK. For a journey that lasts two days and a night you would pay around RUB 5,070RUB (£52.25) for a ticket bought two days in advance.
In Moscow and St Petersburg there are plenty of leisure activities. But if you want to go out to the theatre or ballet, or to the cinema or concerts take a lot of money with you because they are expensive! In other Russian towns cultural activities like the cinema are also expensive. On the other hand, the Museums aren't very expensive, particularly those in provincial towns.
If you would like some less expensive cultural activities then check the Russian universities' programmes (they often have theatre or concerts that are worth trying).