[greenyoda]

I'm guessing you already know this, since you're referring to "urad dal" by its native name and buying it in large quantities, but others might not:

Here in NYC at least, foods like beans, lentils, rice, spices, etc. are much cheaper when bought in Indian food stores (where they're everyday staples sold in large packages) rather than in regular supermarkets (where they're sold in much smaller packages).

There are similarly good deals to be found in Chinese and other ethnic grocery stores.