In my opinion, that is over priced. Unless you have reason to be in Santo Domingo (job, school, etc.), you are better off being just outside the city. You can always go in to shop, dine, or party.
Why not stay at the beach (Boca Chica), just 15-20 minutes by car from the outer edge of Santo Domingo. A 2-bedroom (unfurnished) house in a quiet and clean neighborhood go fro about RD$5000/month (US$300). A very small 2-bedroom furnished house in Los Coquitos will run about RD$2500/month (US$150).
A furnished luxury apartment (2-bdrm, pool, air, etc.) will run about US$750. Example - Bella Vista, Boca Chica:
Also, about half of the hotels in Boca Chica have apartments that vary from studios to 2-bedrooms. Most will work out special pricing for long-term renters (up to half off), putting them in the range from US$400-800/month.