Sorry no one has answered your question here.
To get a mortgage in the DR, it is normal to pay 30% to 35% down. Unless a bank is pushing a special rate, or you have really strong credit established here in the DR, it is very unlikely to get a mortgage with less than 25% down on a property. Financing can be gotten through either banks, such as Banco Popular, or the Savings and Loan (Ahorros y Prestamos) organization here.
Recently rates have been running from 14-16% and upwards on a peso-based mortgage. This depends on your credit, and your equity in the property. The good part is that after a couple of years of normal devaluation of the peso, the payments become easier to make.
There are mortgages available here in US $ terms, but harder to find. I have a dominican friend who got such a mortgage about 2 years ago, at 9% for 7 years. Peso mortagages were then running about 26% I think.
Walk into the main office of Banco Popular and ask them what is necessary to get a mortgage. Other dominican friends have told me that it is easier for a foreigner to get a mortgage, but that may just be misguided jealousy talking too.