Bangkok is awesome... 18 hours,, eh, lol kinda pushin it... The trip from the airport to downtown Bangkok is about 45 minutes if I remember correctly (without traffic)... You'd have to exchange money when you get to the airport, and when you leave the airport be prepared to pay 500Baht for departaure tax, that got me and my friend who had about 10.00 left hahaha, so we were screwed... As for hotels, you can find any hotel for under 100.00, you'll live like a king for 100.00... Things are very reasonable in Thailand... Depending on what times you arrive and leave, you might be able to squeeze in some sights.. The Grand Palace is really cool, a lot of things to see, probably take ya about 2 hours to see everything.. If your into nightlife, you should DEF. check out the nightlife over there... It's like the Asian version of Amsterdam if you get my drift crazy experiences haha... It's a lot of fun though... You'd probably be able to do a lot in 18 hours...