This was an interesting question proposed by a "god" fearing man in his mid 30s on the same train. The question was directed at his fellow passenger. The hawker/vendor in question was a man in his 20s selling liquor tea (black tea) with some spices and lemon.
His steel pot could hold roughly 350 cups of tea which he refills at least thrice a day. To make one such pot of tea, he requires about 850 gm of sugar and 50 gm of cheap CTC tea. These items cost about INR 50. The costly item is the masala or the spice which is a strange mixture of salt and assorted "stuff". This masala is made by the vendor himself and apparently costs about INR 80 / kg. However he can barely finish 100 gm of it per day. That brings his daily investment down to INR 8. Then there are the lemons which during the most expensive times of the year will not cost more than INR 1 per piece and he uses some 25 of them a day. Along with this we must also include an overhead of INR 50 which goes into the serving cups, license and miscellany. His total investment never exceeds INR 235 for the whole day. His three pots of tea sells for INR 3 per cup and comes out to be INR 3150 per day which is roughly about INR 2875 profit /day. For 30 days it comes out to be INR 86250!!!!
These guys earn way more than me and my kin - a PhD student. Our government as well as egoistic professors of our institute are not competent enough to understand the financial hardships we have to go through.
Well, the estimate was a bit blown up. Realistically these chaiwalas make about half of that. This is usually attributed to occasional poor sales and a huge unpredictability factor. However, at a realistic earning of INR 40000 per month, the conclusion is still valid - that these guys earn way more than me and my kin.
Edit : There is a small follow-up presented here : http://54uv1k.blogspot.com/2011/04/follow-up-to-chaiwala-on.html