I think the price varies greatly depending on how prestigious the office / doctor you go to is. Either way is way cheaper than in the US. For instance my son's braces were going to cost me about 1,500.00 USD if I had it done down there, which is less than half what they cost me here in the US, even after insurance covering part of it. I still got it done here in the US, just because with those you have to have them checked every so often and the dentists here will not do it, if the original work was performed in a different country.
One more thing: You should understand that while the cost of any medical / dental procedure is way cheaper in the DR, there's also no recourse if the doctor/ dentist screws up. This has happened a few times with foreigners who go to the DR to have liposuction procedures performed, because of how cheap it is. A few of them have died...and I'm pretty sure the families have not gotten a penny out of it and the "doctors" are still practicing.