My girls are having Ballet lessons at The Boys' & Girls' Clubs Association of Hong Kong (South Horizons), the principal and one teacher/assistant will be teaching at the same time, quality is acceptable and children are gonig to take Royal Academy of Dance Graded Examination, I'm satisfied with their results too.
Fees are reasonable, the course have subsidy from the government, around $600-700 per month for beginners (English medium is not this price, a bit more expensive) (higher grades: $800-900 per month).
I think SDM is a bit expensive to me and their classroom is too dark, and I often see only young children (3-5 yrs old) having lessons in it, few of them are older children at higher grades (Grade 4 or above).