As you are open to buying diesel cars, I would suggest, keeping in view your run of 2000 kms per month, you can consider Indica V2 Turbo.  It will cost between Rs.4 to 4.5 lac depending upon the version you choose to go for - most popular/preferred is DLS (BS III), which may cost you around 4.25 all inclusive.  It will give a mileage of 16/18 in city & 20/22 on highway depending upon the driving condition/style.  The mileage would drop by 10% in city with AC on & less than 10% on highways (like in all cars).  It's a very sturdy, comfortable & spacious car.  It's road grip is fantastic & AC very powerful.  This turbo model is virtually as good as a petrol car.

Else, you could consider WagonR DUO - it's a good car with low running cost (better than Santro CNG).  Logan (Diesel) is a very good car - better than the 3 referred herein above, but belongs to higher segment.  It is more spacious & comfortable (compared to Indica Turbo). It gives a mileage of 15/17 in city & 20/22 on highway.

But all in all, I feel Indica Turbo is the car for you.