You will get best mobile phones under Rs 20000 in India. You can choose any from them and then buy your best and simple phone under Rs 20000.
These Mobile phones are available on popular E-commerce sites like Amazon, Flipkart etc. So You don’t need to go to local retailer store.
However, I will suggest you go to near retailer what if they are selling at low cost then you can save your little amount of money. Now, brands are competing with latest specifications and they sell their smartphones exclusive on e-commerce sites.
But if you know someone where you can get these mobiles phones offline then try to bargain as well.