Boat rides is S$9/way to and fro Sungei Rengit from Changi Jetty by bum boat. Last boat leaving Sungei Rengit at about 4pm but must reach jetty early as the boat operator needs 13 people before leaving.
There's also ferry by Penguin to Sungei Rengit now at scheduled timing from Tanah Merah Terminal at S$36 for 2-way. Last ferry from Sungei Rengit at 6pm but must reach jetty 1hr before departure.
Taxi is now at RM20/way from the jetty to the town of Sungei Rengit, can share cab with others if you have less than 4 as most people heading to the same place named Si Wan in Chinese. Within Sungei Rengit, all shops and restaurants are walking distance and you just need to go to the taxi station to get a taxi to the jetty.
Bum boat service from Changi Village to Pengerang is S$7, $2 more if you bring your own bicycle. The first boat leaves at 7am, travelling time is about an hour. Hand over your passport to the bum boat operator who will take down your particulars. Once he has registered 13 passengers, he'll lead you through Singapore immigration and to his bum boat.
You'll have to fill up the Malaysian arrival card. Ask for one from the bum boat captain. ; )
You'll go through the Malaysian immigration after you arrive. A few taxi drivers will approach and ask if you need their service. It cost RM$6 per person to go to the heart of Kampung Sungai Rengit. But if you're travelling in a group of 4, it's RM$20 per trip.
The taxi drivers are generally friendly and you can ask him/her about the town and its surrounding attractions! You can also arrange for the return trip back to the jetty after you've finish wandering around town. You can pay them on the return trip. (They're not afraid that you might run away without paying them. Everybody knows everybody there! Haha!)
There's a few seafood restaurants in town! Lobster is the main attraction! There's also a confectionery where you'll find traditional chinese cookies freshly baked there. A local tit bits shop selling all the local food products. For those who can only eat in air conditioned place, there's a Marry Brown Fried Chicken there too!
On your return trip, you can request your taxi driver to let you make a quick detour to a mango farm where you can buy mangoes or any other local fruits that's in season.
The bum boat ride back to Singapore cost $RM10 per person!