Ko Laan' (or Lan or Larn, or Coral Island) is 7.5 km west of Pattaya. It covers an area of 5.6 sq. km and has six popular beaches with a decidedly "touristic day-trip" flavour.
Regular ferries from Bali Hai Pier cost 30 baht at April 2014. Takes about 1 hour. The pier is located near Pattaya Walking Street in South Pattaya. To get there, you can hire a songteow, and the fare will depend on the distance and number of people. From where the bus from Ranong to Bangkok stops, the hire was B150 for two persons, which was reasonable considering the distance. The ferry will take you only to the main pier in Ko Laan, and not to any of the beaches. If you are coming directly from Bangkok, take a minibus from Victory Monument directly to Bali Hai Pier.
Once on the Bali Hai Pier, as you walk through, the speedboat operators are first, and the ferry people are at the end before you walk outside again, on the right. Buy your tickets there. Can also be bought before you board the ferry. Note that the ferry times in each direction are VERY approximate (this is Thailand!).
Alternatively, speedboats can be chartered just about anywhere along the main beaches, typically for 1,500-2,500 baht,depending on the numbers. If they got a "full" load, you will pay B300. Or you can book a day trip via an agency. Expect to pay 500-600 baht for minibus collection from your hotel around 09:00, ferry from Bali Hai Pier direct to one of the main beaches (taking about half an hour), lunch, soft drinks, return ferry around 16:00, and minibus back to your hotel.
In January 2014, the standard return price was 150 baht (less than € 4)
There are songteows which meet every ferry at Koh Laan, and will take you to the beaches. Also you can hire bikes and motorbikes. The songteow cost to the beaches is usually B30, but further beaches cost a little more. They only run regularly from about 10am, so if you want to go earlier, you will need to treat them as a private hire. To get to the songteow start place, turn left from the pier, walk past the 7-11 on your left and a couple of hundred metres further along on your left is where they are.
Near the pier there are good eating places, as well as a 7-11. Prices are quite reasonable. There is one place near the 7-11 where you buy the seafood,and they cook it for you.
Close to the pier is the main "town". There is no beach here, but there is plenty of accommodation. It appears to range from B800, to B1500, depending on how much "luxury" you want. (e.g. aircon). Non aircon should be cheaper.
To return directly to Bangkok from Bali Hai Pier, there is a ticket seller on the right close to where you exit the pier. Tickets on a minibus (limited baggage) are B100, and go directly to Victory Monument without the usual tortuous stops through Chonburi.