2018: You could rent a Thai traditional dress for only 100B at Wat Arun. I had been to Bangkok several times before, but never knew about this, until very recently. So on my latest trip to Bangkok, I took a water taxi to Wat Arun.
There, right after I stepped off the boat was the stall where one could choose from the many different colors of dresses. I picked blue. They helped me put on the skirt, the sash, the brooch, the bangle, the belt, the headgear, and the long nails. It took less than five minutes. There was no need for a changing room; the dress was just wrapped and pinned around me.
Then I was free to go around the temple area to take pictures. I wish I had had some makeup on. The lighting was bad because it was noon and the sun was right above. Of course, when you look like shit, always blame the lighting.