I flew into Luang Prabang, Laos from Chiang Mai, Thailand with Laos Air, arriving at 4.30pm. The flight is little over one hour. 

You don’t need a Visa prior to arriving in Luang Prabang or Vientiane as this can be obtained at the Airport. 

A 30 day visa will cost $35 USD for Europeans & Americans and $42 USD for Canadians.  Just make sure you have some passport size photos and correct change. 

If you pay by Thai Baht they will charge a premium rate of about 1900 Baht when it should be not more than 1400 Baht.