Bar 360 is a small brothel/bar located near the northeast end of the colonial district at Calle Arzobispo 360 between Calle General Luperon and Calle Las Mercedes. It's the only one in the immediate area as far as I know.
I only visited here once in the evening. I initially wasn't very impressed with the lineup, 2 of the 6 ladies were doable, but nothing too enticing. Fortunately, one of the ladies was able to shake her ass and flirt with me enough to entice me to bring her back to my hotel. She wasn't the most attractive, but she turned out to be the best session of my trip. She was also the only one I had sex with more than once.
I only paid 2500 DOP for the all night session, but I think this was an exception. The owner or manager told me I was only paying for a couple hours, but my date ended up staying all night.
Bar 360 is a little out of the way and doesn't have a big lineup, but I recommend the place.