40,000USD is mucho dinero, 1,480,000RDS, I asked my friend at the bank if that was a lot and he nodded yes.
Afgan is partially correct, but that is if the OP wants to go all out. A nice,clean and safe place in DR from what I am hearing is La Vega.
If you want your money to go far. Live like a Dominican, and when I say that, I don't mean to live in a barrio (I heard the snickers already). I don't know who you are but eating a good, healthy Dominican diet, platano, aguacate, yuca, huevos, carne de pollo, name, yautia, papa, pan de agua, chocolate caliente, mucho jugo y mucha agua. These are super cheap and will decrease costs exponentially. The school situation? I don't know, I don't have any kids myself, but my cousin has three kids and they are all starting to go to college now and he seems like he's doing ok. My other cousins kids are also in private school and it's expensive for him but it doesn't seem to be breaking them either.
40,000 is good if you go partially native, so like AZB says take it easy....
Don't fritter your money away on too much eating out and you should see lotsa money saved in the bank. Then you can enjoy going to the natural parks which are not that expensive and many cases free.