COST OF 1ST CLASS SLEEPER (SPALNY VAHON) FROM kIEV TO lVIV

You can check www.uz.gov.ua

The ukrainian railways. There is no English however. The easiest way is this. On the left side there are some links to clicks
Click on "Ціни та наявність місць по ст.Київ-пас." Prices from Kiev. Now you can choose your train. You must know the train number, and hopefully the spelling in Cyrillic for Lvov and Kiev. For exampel the train No 7, Kiev - Chop, depture time 2358 from Kiev will cost in SV львiв 394.06 Uah. If you want more information about trains. Train 081К київ пас -ужгород also goes Kiev - Lvov, it terminates in Uzgorod, close to the Slovak border. Here the ticket will cost "львiв 477.26"

I hope that is was to some help.

You cannot book the tickets in advance through the web. It must be done at train station. A better alternative: There are in bigger cities travel agencies, who also sell train tickets, do not expect anyone to speak English. It will, however, be done in a much nicer enviroment, than Kiev Pass, who is a horrible place to visit. They will surcharge you maybe 15 Uah, but it is worth it. It is a called "UZ-Kasa", "zalichnitji kasa"

Well, actually, you can book tickets in advance online, just not so much in advance; besides, unlike Russian railroads, Ukrainian Railroads charge a small sum for it. Go to http://www.e-kvytok.com.ua/wps/portal , there is a possibility to see part of the site in English (click on "English"). The interface will still be in Ukrainian, but you can use google-translate, if you need. To buy a ticket you will need to register, and when you do this, there will be an instruction in English. Stil, you would need to know the Ukrainian spelling of Kyiv and Lviv to buy tickets or check prices. You would get a form with a specific code (numbers and Ukrainian letters) that you need to either print out or write down and give to the cashier at the booking office at any Ukrainian railway station.

it's better to buy directly on the train station, i think they sell in advance for 3 months or so.
You can arrive to kiev or lviv and just ask how to get to the train station on the reception and ask them to write how many tickets you want and a date when you want to leave the city and with this paper just go to the ticket office and they´´ll sell you tickets.