There are many, many threads about this very subject. Do a search or just screen thru the pages and pages of info.
Dominican health insurance is indeed cheap, when compared to most expats' countries of origins.
But coverage is somewhat limited and most always requires a hard to predict co-pay. Still, these co-pays are usually lower than anywhere else and the insurance card gives one the additional advantage of being treated as a "normal" (like in "local") case and bypass the "hustle the gringo" part from the get go on.
But, there may come a time, where you prefer to bypass the insurance and cut a cash deal with a provider to secure a preferential or better than insured treatment.
Try to stick with one of the MAIN insurance companies like UNIVERSAL.
Some associations and clubs offer group policies to their members... there is one in Sosua who does.
... J-D.