Cheap, Cheapish, and not cheap at all.

In Bangkok the most expensive mean of travel is the tuktuk. They have no meters and their drivers always quotes 200 baht (5$) irrespective of your travel distance, because (I suspect) the Lonely Planet advices that no ride should cost more than 200 baht. Paradoxally, the luxury taxis are cheaper. Cheaper still, is the metro, which at first glance looks like a fake-copy of the one in Delhi. The least expensive are the boat buses which races around the canals of Bangkok. Most Thais dislike them because the powerful rip waves from the boats often crashes on walls of the canal, spraying of sweage-water back at the boat. Yum. The more daring Thais are provided with a traffic-free commute into town, and with entertainment whenever a foreigners falls over, so it's all good.