Like Hillbilly said, you can get the services you need in Santo Domingo and Santiago.
If you have insurance in the US, keep it because with your condition you are unlikely to get it here. Check with insurance company to see if they pay direct or if you must pay and submit claims for reimbursement.
Regarding price, to say it is very expensive here without knowing what you are paying now is not a good way to respond to your question. If you live on the local economy it seems expensive, but compared to what you pay for somethings in the US, for example, it isn't. My wife, for example, recently had a hip replacement that cost much less than would have been charged in the US.
Your question about cost can't be properly addressed without knowing what you are paying there for the monthly CT scans