whats the cheapest way from the airport ( Bangkok) and most convenient way from the airport to one of the River hotels? How much and how long does it take? Thank you .

The cheapest way is via taxi. Go to the taxi stand, it will be about 350 baht plus tolls (about 75 baht, if I remember correctly). You do want them to take the toll road (the driver will ask and will tell you the tolls are extra).

How long it takes will depend on the time of day you are arriving. The typical time it has taken me to or from the airport to the Royal Orchid has been 20-30 minutes. If you are across the river at the Pen or the Marriott or the Hilton Millenium it will take longer and cost a bit more.

I like to use one of the limo services as we usually have lots of luggage. If there are more than two of you or if you have large suitcases, consider the limo services. "Limo" here means a sedan like a Mercedes. We use AAC Limo and the approximate price is 1000 baht plus tolls. You get a discount for booking roundtrip.

I have a similar question. We are a family of four (2 kids and 2 adults), we'll have probably 4 suitcases + 4 carryons.

Will we fit into a "limo" (mercededes sedan) or do we need to look for something different.

My plan was not to book ahead, but to find the airport limo service with the hope that they have minivans if needed.

Is this a doable scenario?

ktal
You should be able to get a van upon arrival. Sounds like that's what you need with four of you and all your bags. It's probably better than two taxis, which is what you would otherwise require.

MarieB
Taxi is the cheapest way, by far. But if you are arriving for your first visit to Bangkok, you might feel relieved, after arriving, to find someone looking for YOU with your name on their signboard. Up to you. AAC Limo would do that.

Actually, the cheapest way for one person is the airport bus, at 150 B, but if you have any luggage, it's not the best way.

Note that the airport "limos" are not limos, they are ordinary cars. The Airport Limo service has Toyota Camrys, London Cabs and Isuzu SUVs, in addition to other types. They'll have someone for a family of four, for sure.

ktal, I wouldn't count on being able to get a van upon arrival. You often can, but in this case, it makes sense to use one of the limo services to reserve a van. AAC does this, and the only limo service at the airport, AOT does this as well. Arriving with two kids and not having ready transport sounds pretty unpleasant, especially after you've all been flying for so many hours.