If you want 'solid speed and performance' in least price, get Windows phone.
Check Lumia 540 dual sim specs, available for rs. 15000, twice faster than 1GB ram laggy Androids.
Still camera and display is better than Grand Prime, but no HD video recording. Battery timings are very good too.
I got Lumia 430, the most basic Windows phone and it turned out to be faster and lag free than Grand Prime and S3 [emoji1]. Windows 10 mobile is releasing very soon, which is very much better than Windows 8.1. They have highly customizable UI.
https://www.pakwheels.com/forums/showthread.php?p=4874835
But if budget is 20000+, then get a 2GB ram Android phone.
Use camscanner or any scan app from play store. They scan pages just like a real scanner.
On a side note, you can use Roehsoft ram expander app to increase ram using SD card on rooted phones. It makes the phone lag free, but battery consumption gets higher.