I have transferred money from the US to the DR - and back again without any problems.
You should do it like this:
1. Get a local bank account in USD. Get it at a strong bank (NOT baninter).
2. Ask the bank for the wire information to make a transfer. They may even give you wire information that goes to a US bank, with a further forward to the DR bank. The advantage in this is that domestic transfers cost less.
3. The money will be in your account in 2-3 days.
My cost for this is US $15, no matter how much money.
Do not transfer via a check, those take something like 40 WORKING days to clear over here. Terrible! The amount you lose in interest is not worth the $15 you save.
To send money back, go into your local branch and tell them you want to make a transfer. The charge to send is $40, no matter how big the quantity. Again, it takes two to three days.
However! I would be cautious about keeping more money over here than you need. The DR appears to have low USD reserves right now and they may well put restrictions on how much money can be transferred back. You won't lose the money, but you may be forced to exchange for pesos like I was (see the thread in the living forum, "baninter problems".
If you need money in the DR, just withdraw USD from your US bank account and take it to the best exchange place you can find. Western Union and (particularly) Coffeesport.com have consistently had the best exchange rates in Santiago. I wouldn't bother with changing on the street, some locals may do it, but the chances of getting ripped off are high and the rates not much better (if it all).
I found the bank transfer process has worked very smoothly for me in both directions when I did it this way.
Adrian