Although there’s more agencies than necessary in Bangkok which will readily offer an inexpensive trip, you can get to Damnoen Saduak on your own by public transport. To do so, head to Southern Bus Terminal, where you’ll find the bus #78 leaving every 40 minutes, starting at 6 am. As usual, use your body language to ask for help getting off at the right place. Ticket price is 64 Baht each way.