Here is an overview of all kinds of transport by busses, songteaws and boats to and from Chiang Khong to surrounding places as well as to Chiang Mai and Bangkok.
Border crossing between Chiang Khong (Thailand) and Huayxai (Laos) is possible daily between 6 am and 6 pm. Entering Thailand means getting a 15 days tourist visa in form of a stamp in the passport. Entering Laos means normally getting a sticker in the passport, including a 30 days visa. Here the rules are different for different nations. The fee is between 30 and 35 $ US. On weekends and holidays the Laotian authorities charge one $ US extra. Swiss citizens get a 14 days visa for free.
At least every hour, sometimes every 30 minutes from the early morning on. But, the last bus in the afternoon already departures at around 4 pm.
Two busses daily.
1. Departure: 8:20 am, arrival: 2:55 pm, Type X, 272 Baht.
2. Departure: 1:00 pm, arrival: 7:50 pm, Type A, 211 Baht.
Two busses daily.
1. Departure: 6:00 am, arrival: 1:10 pm, Type A, 211 Baht.
2. Departure: 10:30 am, arrival: 5:20 pm, Type X, 272 Baht.
Every day incl. weekends and holidays.
V: VIP busses are equipped with big seats, snacks and drinks are served. Their is a toilet on the bus.
X: X Class bus is all the same as VIP bus, but the seats are smaller than on the VIP bus.
A: A Class busses have economy class seats, no toilet and no snacks and drinks are served.
You can buy the ticket at the bus station. Operator is Green Bus Thailand.
There is at least one bus to and fro Bangkok's Northern bus station and Chiang Khong.
Frequently between 6 am and 6 pm on longtail boats. For vehicles (motorbikes, cars, trucks) there is a bigger ferry, also frequently running.
Every morning at around 11 am there is a slowboat going from Huayxai (Laos, on the other river side of Chiang Khong) to Luang Prabang. It needs two days. Therefore there is a stopover in Ban Pak Beng, a hamlet in Laos. Next day it continues at 8:30 am. Buying a ticket in Chiang Khong costs 1,100 to 1,200 Baht. If you go in the morning to Huayxai to the box office, you can get it for 900 Baht (requires negotiation, ask for 900 Baht, the official price is 1,100 Baht). The boats are pending to and fro, so it's the same game in Luang Prabang. There is no need to to book accommodation in Pak Beng in advance, because it's easy to find a place to sleep there and cheaper to do it there. You can get a lively impression of the slowbaot trip watching the movie 'On the Mekong'.
Speed boats are available as well. Best to book a speed boat in Huayxai. Shouldn't be more expensive than 1,800 Baht. They are small, fast, and make it to Luang Prabang in one day. Therefore they are uncomfortable and, more than that, not unperilous. The Mekong River is not easy to navigate.
There is a daily Songtaew (a small, open kind of pickup with a roof and space for twelve to fifteen passengers) to Chiang Saen (60 km). It starts at about 8:30 am a bit North of the Seven-Eleven near Greenline Guesthouse. The songteaw stops at Baan ... where the passengers change to another one, continuing to Chiang Saen. It costs two times 50 Baht. The drive is scenic, along the Mekong River banks at the foot of the mountains. Be aware of that it might not go if there are not enough passengers.
From Chiang Saen there is a following connection with another songteaw to Mae Sai at the same day. Alternatively Chiang Saen can be reached by bus via Chiang Rai, in case the songteaw from Chiang Khong does not go.