Sree's is probably the cheapest place to eat downtown and still feel like you're getting a great deal. There are lots of cheap places downtown, but they usually leave something to be desired. Not Sree's!
It's $5, and you get Tamarind Chicken(at least every time I've been there, that's the only meat option, but it might change..) a vegetarian option over rice, with a piece of Naan. The owner (Sree) runs the joint, and he'll tell you what to try and what not to try.
Definitely worth the lunchtime walk. I only go once or twice a month, due to the real or perceived lack of variety.