Congrats Jtm,
I recommend Dr Hon, his clinic is located in Central and he can do those tests for you. He's happy to see you ( think he may be one of the few) for prenatal appointments or one-off scans, even if you're not using him for delivery in a private hospital.
Number is 2899 2293. I would call soon as he can't take appointments with less than 2 weeks notice.
Unsure of the cost as I'll have my tests at the hospital, but an ultrasound was $2300 for me. My friend who has had her baby said her appointments with him were never over $4000.