My fav joint where you could get good food below Rs.20 has to be the vada pav joint outside the CTO located opposite to the High Court and facing Hutatma Chowk in Mumbai.
You get a piping hot vada pav just for Rs 5.Two vada pavs and you feel quite full.You also have the option of going for just the batata vadas if you so desire. The vadas are always served hot with dry powder garlic chutney. Fried chillis are also given complimentary.
After having the vada pavs, you could cool off with a glass of sugarcane juice available right across the foothpath.Full glass of sugarcane juice would cost Rs.5 and half glass Rs.3.Ginger is also crushed with sugarcane giving it that tangy feel.
For about 15 bucks you could have your fill and proceed to your workplace satisfied.