You may be better to re-post this in the legal section where the resident dr1 legal advisor may see it and answer.
Depending on your nationality you need to also investigate the second passport/citizenship route as some countries do not like the dual passport method without relinquishing one, as well will you have all the same rightful respect from our origin country in the case of worst case situations.
Different lawyers will provide different pricing so you will have to check on that or rely on others to say what they recently paid.
With residency, you have to renew periodically. Either in person in Santiago or in Santo Domingo. Depending upon how long you have had residency, you can renew for 2, 4 or 10 years. Of course if you have citizenship you don't have to renew it. To become a citizen, first you have to be a resident.
A resident can only be out of the DR for 6 months without special permission or you forfeit residency and have to start over.
Residents cannot vote.
Reportedly a citizen can post bail if charged with a crime, but a resident cannot. I find this hard to believe but do not have direct knowledge regarding this point.
Others have indicated that there are different policies on taxes between residents and citizens, but I have no knowledge of those differences if any.