I live in Argentina part of the year, and a native Kentukian btw
and could recommend Buenos Aires as a very good choice for dental work. Really depends on what you need done and the amount of time you can devote to your visit. I have had some cosmetic work, veneers, and crowns and general cleaning etc performed here and with one exception ( bad crown) have had very good luck. But as in any city, there are some good dentist, so so ones and some really bad ones. The ones that tend to garner the dental holiday customers tend to charge higher rates. However, offices are plush, they tend to speak English fluently but do provide good dental services.
I think I paid about $200 usd for a porcelain crown and $350 usd for a crown and root canal.
Sam