The OP asked how much it is to live in Santo Domingo, and with a lot of respect, Boca Chica is 40 mins drive from Santo Domingo and a completely different place.
In Santo Domingo I would set a budget of about US$1,000 to rent an apartment, that will get you a reasonable condo in a safe area. US$2,000 will get you somewhere nice in a top-end condo. Supermarkets and restaurants in the capital are now way more than the US and I think you'll need at least US$ 500 for food and drink. And I'd probably suggest about US$ 100 a month for electricity. I have three apartments in the capital and even though we try to keep the electricity usage down as much as possible it's always clocking in at a minimum RD$ 6,000. Fridges, AC's and Inverters all use a lot of power.