For Bangkok hotels & cheap guesthouses There are hundreds if not thousands of places to chose from. The great majority of the really cheap guesthouses are on Khao San rd. There are also large concentrations of Bangkok Cheap Hotels on Sukumvitt near Nana Station on the BTS, and Patpong near the Silom Station on the BTS. You will also find guest houses and cheap hotels near the Bayoke towers and the Siam Square area also just off the BTS.
For cheapest Bangkok hotels accomodations the best area in my opinion for things to do and comfort and value, is between the river and Khoa san rd. You get quiet with lots of small cheap restaurants and you are close to the boats on the river. The Khoa Shan rd stop is 13 which if you take to stop 1 will get you to the sky train and the rest of Bangkok. The budget accomodations in this area tend to have little gardens or sidewalk cafe's which are nice a great little restaurant to look up is Hemlock, get there early as it fills up nightly.
Suhkumvitt I always stay at the Thai house inn a Bangkok cheap hotel that is very friendly and in a great location 50 meters from the Nana escalator for the sky train.
For Patpong hotels try the strand a boutique hotel with great ambiance just off the strip & bars area yet very quiet
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