Udon Thani airport is the cheap way into Laos: low-cost flights from Bangkok, then the Naluang international bus (07:00 and 09:00, ฿155, 2 hours to Talat Sao) or an airport van straight to Vientiane (฿470–700). The morning train from Udon crosses the bridge to Khamsavath for ฿117–333. Visa, bridge and what each option costs.
The morning train from Nong Khai crosses the Friendship Bridge to Vientiane Khamsavath in 30 minutes for ฿70 (third class) or ฿120 (air-con); the Naluang international bus goes to Talat Sao in the city centre for ฿122 four times a day; or do it yourself by tuk-tuk, the ฿20 bridge bus and a Lao taxi. Every step, with the visa.
The red local bus from Chiang Rai Terminal 1 runs to Chiang Khong every hour or so for ฿65–90, about 2 hours; then a ฿150 tuk-tuk to Friendship Bridge 4, the ฿20 shuttle across, Lao visa on arrival, and a tuk-tuk into Huay Xai for the 11:00 slow boat (฿900 at the pier, 2 days to Luang Prabang). Every step with prices.
The direct Lao Airlines flight takes about an hour; overland packages sold from Chiang Mai (van to Chiang Khong, border, Lao sleeper bus) take 20–24 hours for ฿1,450–1,820; the three-day slow-boat route via Chiang Khong and Pakbeng is the classic. What each costs, and which suits which traveller.
Train 133 leaves Krung Thep Aphiwat at 21:25, stops 40 minutes at Nong Khai for Thai exit stamps and arrives at Vientiane Khamsavath at 09:05; second-class berths ฿784–874. The 08:45 day train arrives 16:35. Lao Airlines flies it in 70 minutes. How the border works on the train, and what Khamsavath station is like.
Through minibuses and coaches run Bangkok–Siem Reap in 8–9 hours for ฿500–1,100; the 05:55 train to Ban Khlong Luk costs ฿49 and puts you at the Poipet border by 11:20, then it is $9–12 for the last 150 km. Visa, the border walk, and the scams to walk past.
Malaysia Airlines, Thai AirAsia, Scoot and others fly Bangkok–KL in 2 h 10 for ฿2,800–4,500 booked ahead; the rail route is a sleeper to Hat Yai, a shuttle to Padang Besar, immigration at the station and the ETS to KL Sentral — about 24 hours over two days from ฿1,300; the through bus is 20+ hours and no cheaper. Border, visa-free entry and the Digital Arrival Card.
Thai AirAsia and Thai Vietjet fly Bangkok–Hat Yai in 1 h 25 for ฿1,047–1,857; the southern sleeper trains take 15–17 hours from ฿310; from Hat Yai, minivans cross to Penang in 4–4.5 hours for ฿450–500 and the Super Nice VIP bus is ฿328. How the Sadao border works, and the train alternative via Padang Besar.