There is a very good road from Lao Cai to Sapa, it is 38 km. Everyday, there are lots of tourist buses and taxi to transfer tourists from Lao Cai to Sapa and return. It costs around 2 USD for a sharing tourist bus ticket and 18 USD for a private taxi or van.
You have two ways to go from Hanoi to Lao Cai and Sapa. First, you can take the trains. There are many travelers like this way because it is safe and they can enjoy the nights trains, so you can save your time when traveling. You can book the tikets through the website of Vietnam railways at http://www.vr.com.vn, or many companies offer tickets service as: Fansipan Express, Ratraco, Tulico, Et Pumkin, Victoria Express, Fansipan, Royal... There are different level from classic to VIP cabin (they serve water; food; fruits; air conditioner; luxious bed and all have staff to take care of the clients.), so you can easy to choice. The price cost of you from 20 - 40$/person, Victoria express train is much more expensive and only offer guests stay at Victoria hotel, it is about 160$/person.
King Express train (photo collected)
Sleeping bus (photo collected)
Second option: You can travel by buses. Since 21 Sep 2014, after the highway from Noi Bai airport to Lao Cai city completed, it is take of you shorter traveling time (only 5 - 6 hours). After that, there are many tourist bus companies collect from Ha Noi to Lao Cai and Sa Pa such as: Ha Son - Hai Van, InterBus Line, Sa Pa Express, Fansipan Express... And also have different option for you such as: Limosine VIP bus, Vip soft seat bus, sleeping bus, sleeping bus with VIP cabin. The price cost of you from 10 - 25$/person.
Update by Thanh Tuan