Is there a cheap way to get from the airport at Prague to downtown?
I would recommend Mike's chauffer's service, good price and easy to use.
The cheapest way is public transport. Bus #119 to Dejvicke namesti (it's the end of line) then subway. I think it is 26 crowns (about $1.40).
I third the public transit. It was super easy and cheap.
I second the public transport route. It's cheap, efficient and gives you a good introduction to the city.
I've used this company on two different trips to Prague. Both times I went roundtrip from Airport to Hotel. Dependable, affordable and owners are American Transplants so they speak very good English.