I booked a flight from Vientienne to Pakse and the cost was 125.27 US one way.
It is obviously high tourist season as any of the guesthouses I checked were fully booked. I ended up having to change accomodations three times while in Vientiene as most only had 1 night availability. II am not pre-booking any rooms but being that it is now high season in Laos it would have been a good idea to book rooms before arriving. I have not had this problem in Cambodia and Vietnam. I was paying approx. 150,000 kip per night (without breakfast). I found Vientienne to be a very organized city with many interesting sites to visit but sooo hot and humid (beginning of March). I walked to most places that I visited as my room was quite central. I again did the walking tour outlined in the Lonely Planet and visited the Wat Si Saket temple, Pha That Luang as well as the Patuxai monument said to be reminiscent of the Arc de Trionphe in Paris. I also visited the Lao National Museum (quite military and politically oriented). Vientienne has everything of a modern city including great coffee and pastries!!