Nobody has ever made an extension on DTV yet, because the Visa ist just 102 days old. There are no official announcements from the Immigration yet, no known details, but you knows it for sure...? Okay... but I dare to doubt that...
P.S.: It's not even officialy considered as a "Tourist Visa"
No new payment on re-entry, many people left/re-entered already and can confirm this. The fee is a one time fee. Another thing is the extension inside the country... not clear yet what exactly will happen about paperwork and price, we have to wait a little bit more. The oldest DTVs are just 102 days old... so... no extensions yet...