Tamil Nadu is one of the good places to buy agricultural land. Normally, the lands very near to the roads are quite costly, with rates going up to Rs. ten lakhs per acre. However, if you go a little interior, you can always find lands that are much cheaper, at around Rs.5 lakh per acre.
Now, the location, and the most important point of what you want to cultivate. Please do note, only certain parts of Tamil Nadu, are well irrigated, and rain fed. That is, there is some facility for ground water recharge, and there is a huge amount of organic farming already in place.
One such place is an area called Perumbakkam, which is not very far away from Chennai, but also superbly connected by buses. This place is near a place called Araakkonam, which is a major junction on the Chennai to Bangalore route, some seventy kilometers from Chennai Central, and served by EMU and express trains. From here, this place called Perumbakkam is just around fifteen kilometers. You can also approach this place from the well developed town called Sriperambadur, which is on the Chennai to Bangalore Highway..
Please do note that the water is good, and the strength of the sand is also very good in this place. However, please do note that growing vegetables and selling them to the local markets in bulk, is the best possible way to make money. Rice cultivation is fine, but you need to develop local contacts.
In this place, in the interior areas, land is available at around five hundred thousand rupees per acre. This is a good deal, as you can easily stay in a neighboring village, or build a small house (a one room and a kitchen, with a toilet) to stay, whenever you visit the place to do the farming. It is essential to have a good caretaker too.
It is possible that you stay in Chennai, and find the laborers from the local area to support you. If you have someone in the family who can stay on in the beautiful environment, that would be fine.
Alternatively, areas near a place called Tenkasi, which is a very well developed town, deep South, and well connected to Kerala, is superb for agricultural land. However, this lovely place is not only rain fed, but is hugely agricultural. Hence, land is quite costly here. However, even at twenty hundred thousand per acre, you grow a huge number of coconut trees and develop a beautiful garden too. There are so many who invest in such places, for the sheer pleasure of staying in such beautiful environs.
Much would depend on what you want to cultivate. These are two superb places in Tamil Nadu.