Smartphones now are basically of specifications 4GB 64GB and 4GB 128GB
And also at the same time 6GB 64GB and 6GB 128GB
now the latest trend is 8GB 128GB and 8GB 256GB
So if you want to get smart phone under 20,000 go for the 2nd option.
Which suits your criteria
Majority of the smartphones are Xiomi,Realme,Oppo and Vivo.
Below are the Smartphones under 20,000
48MP+8MP+2MP+2MP rear camera with photo, video, professional mode, panorama, portrait, night scene, time-lapse photography, slow motion | 16MP front camera
16.2 centimeters (6.4-inch) AMOLED screen display with 2400 x 1080 pixels resolution, 408 ppi pixel density and 16M color support | Gorilla glass 5 | DC screen dimming 2.0 | 90.7% screen to body ratio
Memory, Storage & SIM: 8GB RAM | 128GB internal memory expandable up to 256GB |
Dual SIM (nano+nano) dual-standby (4G+4G) Android Pie v9.0 based on Color OS 6.1 operating system with 2.1GHz MediaTek Helio P70 octa core processor,
ARM Mali G72 4000mAH lithium-polymer battery 1-year manufacturer warranty for device and 6 months manufacturer warranty for in-box accessories including batteries from the date of purchase
Box also includes: Type-C Cable, Sim Tray Ejecter, Pre-applied Screen Protector and Protective Case, Booklet with Warranty Card and Quick Guide