We moved here in our early-mid 40s with three kids (at that time just turned 8, 11, and 16), 2 cats and a 100lb dog. There are quite a few families around but you'll find that the DR is definitely more expensive than most developing countries. It IS possible to live frugally--especially if you are willing to NOT live in a bigger, nice development and shop in the outdoor markets. We rent and pay a premium for perceived safety (note: PERCEIVED) and the ability to liquidate rapidly and leave if we so desire. With the amount we pay in rent, we could easily buy some place but we have too many friends who haven't been able to sell their houses/condos and don't want to be in that situation. It isn't like we are planning on running off the island with a moment's notice...rather dh's job is thru a NY-based company and one can't predict what will happen.
(For general info): There are many college students here taking advantage of the fact that med school, dental school and other programs are a bargain down here. Most of these people are not buying houses or condos--although I suppose there are some. The fact that they can rent cheaply on the Malecon in SPM and take guaguas or motos to the university helps. However, most of the med/dental students I know are really quite ready to leave for their internships/residency (PGYs) after being here and don't want the hassle of having to sell real estate or they can't afford a down-payment.
There are many ways one can avoid huge bills here: don't use AC, shop at the local markets, eat/drink local (for example, if you like Vodka--you'll pay much more than if you switch to Rum), live like a local, take advantage of the local outdoor activities (the island has many wonderful natural attractions)... One thing we've refused to compromise on is whole grain products. So, we pay substantially more for "arroz integral" and "pan integral" and have to buy it in smaller quantities (because large bags of brown rice are just not available--and IF someone KNOWS of where we can get them, please share the info!!)
Definitely contact JRR (on DR1) for mortgaging info. He's a great guy and works through US lenders. He'll give you the straight scoop on various financing options and I trust him completely. If he doesn't answer you right away, PM me and I'll put you in touch with him directly.
If you have a stable source of US income (SS for example), it is very possible to live at a higher standard of living down here than in the US-- UNLESS your home in the US is paid off so you have few housing costs in the US (in which case, I'm not so sure about which is cheaper because some people grow much of their food in the US and don't spend much on AC or heat depending on their locale; it would depend on where you are living in the US). Other questions you should ask yourself are: how do you feel about bugs and humidity? are you willing to learn Spanish (many people come here thinking they speak it already only to find out that the dialect is quite different)? how do you feel about unpredictable electric (there are several very humorous, but honest takes written on DR1 about this)? does waiting drive you crazy (if so, this island--Latin Amer in general--may be a bit tough on you)...what type of lifestyle are you looking for here or in retirement in general?
Good luck!