When an engine is too small, it will work much more than burn more fuel...so small does not always match economical.
First, try to find one that is manual. Today's car are more economical due to new generation of electronic automatic transmission. But during our 190e's production, I would strongly suggest you to find a manual trans for economical reasons.
Diesel would be the best. Can you import one or find a broker that could do it for you? A Diesel with a manual trans would be the perfect match in my sense.
Then, a 2.3 petrol engine would be the next choice. I drive a 2.6 (6 in line) it is the best engine I have if I compare with my previous 2.3 but, you pay more gaz for the same run.
Its winter for us right now and I do an average of 12 liter per 100 Kilometer (more city than highway) it is about 19.6 MPG (us). During summer it drop to 10.5 liter per 100 kilometer (22.4 MPG us).
FYI my 1997 e320 with its 5 speed electronic automatic trans was more economical...