Where can I buy cheap rosettastone?

Where can I buy cheap rosettastone?
I’ve heard this is a very useful and helpful language learning software,which you can learn english by yourself.And also its obtained 5 steps of course,like when you learn french,you can start from the very beginning.Simple words such as greetings and easy daily words.Also you can learn italian in this software,it wont be that hard than any other way of learning languages.If you want tolearn spanish,its the same step.But it’s said this software is very expensive,who can tell me where to buy the rosettastone cheaper?