➤ Getting to Ko Kret by the air-con van service

Take the air-con van service (just 10 baht) or public bus 32 to Pak Kret, then head to the ferry pier serving the island. There are no signs in English, and so finding your way can be tricky.

Hire a river taxi, for which touts will quote prices around 500 baht. With enough haggling this may be a reasonable option for a group.
If you can't get a return trip for less than 200 baht (and you probably can't), it'll be cheaper to take a taxi to the temple of Wat Sanam Neua (80-90 baht) in the neighbouring district of Pak Kret, from where ferries shuttle across the river to the island pretty much non-stop for the princely sum of 2 baht (return). Just tell the cabbie "Ko Kret", they will understand.
Getting back is more interesting still, the easy way out again being the river taxi, plenty of which lounge about near the pier. If not, take the ferry back to Wat Sanam Neua, then take a moto or samlor out of the soi (5 baht) to the main street. From here you can easily grab a taxi back to pier, or try your luck with the many buses, minibuses and songthaews heading back to central Nonthaburi and Bangkok. The pier you want to return to is Tha Nam Nonburi or simply Tha Nam Chao Phya in Thai (Chao Phraya Pier).