Screen keeps flickering and jumping from random app to random app......iPad 2 3G wifi 64gb

hi, my very generous sister-in-law gave me her old iPad as the screen had been obliterated and the home button/charger kept playing up (first time I've been forced to use assistive touch! Not fun if you don't know what gestures are! Others have tried to teach me to no avail). Anyway, I've replaced the screen and home button but the charger socket was still in tact and hasn't caused me any issues worth fretting over. I know obliterated screen = issues with digitiser but I made sure the cable was set in a safe way so the screen could fit within its bevel.

Im sure many of you will say "it's not worth fixing! Buy another!" but that's not an option. Besides, being able to afford any iDevice with more than 16GB is a lovely fantasy but I prefer reality and the ol'school fixing it up kinda way of solving device issues. So, with that in mind, what part do I need to replace? If I go to Apple Store, does anyone know how much a reconditioned one is or whether there's a trade-in option? I've got a faint memory that trade-ins and Apple don't mix well. Let me know please????!!!!!!!

frustrated Muma 😠