I have gone to Maekhlong train market with my camera and fisheye lens 8mm,

the cost to go there was so cheap : 46 bahts go and back from Bangkok !

here is a 2 minutes video while the train is crossing :

how to go there :

it's located at 60-70 km from Bangkok center

you have several options, you can get a minivan at Victory Monument to Samut Songkhram

else you can go by train, more interresting to my opinion : (46 bahts go and back from Bangkok)

first check on Internet about the train timetable

then go early to Wongwian Yai train station (the train arround 8am is a good choice)

pay 10 bahts to the ticket office, it's a one hour ride until Maha Chai,

then walk for 5 minutes to the ferry boat : then 5 minutes trip until Bang Laem the other side of the river,

you can walk for 10 minutes, or take a mototaxi to the Bang Laem train station,

pay 10 bahts to the ticket office, it's a one hour ride until Samut Songkhram - Maekhlong market