THB700/kg is if you can bloody find it. It's so rare. You ask people many don't even know this fruit exist. Official name if Thu-Lian-Thet literally "durian from another country".
Only people in the south of Thailand know about this, guess it's close to Malaysia. My southern staff know this fruit and some even grow it at home. People in Bangkok and above no idea this fruit even existed. I've found a guy in Bangkok selling the plant buy it takes 3-5 years to bear fruit and bloody cost 3000-5000 baht per plant.
Like you I also very shock about the price and the fact this is an agriculture country more shocking is people don't even know this fruit exist.