Buses go direct from Mo Chit station in Krung Thayp Bangkok to Sangkhlaburi. The first ones leave at around five o clock and pass through Kanchanaburi on the way.There are also many buses/minibuses leaving from Kanchanburi Bus Station. The trip takes around 5-6 hours and can be up to 7-8 from Bangkok. Tour agencies in the Mae nam Kwai tourist area of Kanchanaburi may also be able to help you get to Sanghkhlaburi by minibus.
Red buses pass through Nam Tok along main road near terminating station for train from Kanchanaburi every 30 minutes. The fare to Sangkhla is 100 baht.
Incredible scenery from along road around reservoir, well worth the 'slow' bus
To Kanchanaburi:
1st class air-con bus: 08:45, 10:45, 14:30 - 4.5hrs, 180 baht
non-aircon bus: 06:45, 08:15, 09:45/10:15, 13:15 - 5hrs, 110 baht
minibus departs from ticketshop at far end of road running from the bus station past the 7-Eleven and the market: 06:00, 06:40, 07:20, 08:00, 08:40, 09:30, 10:20, 11:10, 11:40, 12:30, 13:00, 14:00, 15:00, 16:00 - 3hrs, 146 baht B175 in Sept 2009; not every scheduled minibus actually runs; if full, charge may apply for luggage
car: 3 hours, keep your tank full as fuel is more expensive near the border.
The last bus/minibus for Bangkok leaves the bus station at 13:30, the last for Kanchanaburi at 4 pm.