Seems like a decent ride from reviews on KBB
http://www.kbb.com/mercedes-benz/m-class/2000-mercedes-benz-m-class/
Aside from that, the ML320 gets 15mpg's city and 18 highway. According to fueleconomy.gov, they say it's designed to run best on prem. too
Overall, I'd say go for it. Seems like a...