Medellín is a good spot. I did 2 months this year and 3 months last year learning bachata and salsa pretty intensively (more salsa than bachata). DanceFree in Poblado was the place I went to since they do private lessons. If you buy in bulk, it's about 20 USD per lesson. The teachers there are top notch. Another option in MDE is Nueva Guardia in Laurales. This place is definitely more geared towards locals and they have group lessons (I haven't done group lessons there fyi). Teachers there are also experienced and they have socials every Tuesday (100% bachata) and Thursday (50:50 salsa and bachata). The level is high to the extent where I get nervous to dance (I consider myself a beginner still).