You can find paintings at
Sadar Bazar ( Near Connaught Place)
These are some of the locations I could think off the top of my mind. You can always negotiate at these places and get a painting for as less as 1000 bucks which would adorn your wall.
There are places in champa gali and Shahpur jat and another near indian habitat centre
Local markets has some of the best art pieces. You can checkout nearby areas. Sarojini Nagar, Karol Bagh are few of them.