Which cruise line, which ship? If you look at the brochures or on the website of each cruise line it is all listed there.
If you do not advise us of the ship, the cruise line , and put the word 'please' at the end of your question we cannot help you.
The folk on here are in general knowledgable and friendly. But I guess they are all very irritated by a constant flow of questions of this type. How on earth is anyone supposed to be able to give a sensible answer to this question, unless we know the ship involved, the destinations visted, the length of the cruise and the type of cabin required? Additionally, there is no such thing as "a price" because all sensible cruisers shop around to find the best price.
The starting point is the brochure. Why don't you get one.
Depends on which ship/cruise line. Some of the older ships have a few single occupanct cabins but most of the newer ones do not. You can have single occupancy of a cabin designed for 2 but there will be a single supplement. these vary considerably from about 50% for the less popular cabins/cruises to 100% plus for the better cabins. if you speak to a travel agent specialising in cruises they will be able to tell you which cruises have more reasonable supplements or single cabins. Alternatively if you have a specific ship in mind you can check on theri website or the berlitz Guide to cruising if the ship has any single cabins.
Like all holidays for singles, it always works out more expensive than if there were two of you sharing the cost. Don't let that put you off, I've cruised many times on my own and find it the best kind of holiday to do on your own.
Good luck finding something suitabl.