How annoying is it to use with the line on the screen? Is it off to the side and towards the middle?
You can get a refurbished iPad Mini 4 direct from Apple for $309. Those do include a 1-year warranty and new battery. I would weigh that cost versus the screen replacement cost.
Refurbished iPad - iPad mini 4 - Apple
If this happened to me, personally, I would probably keep using it and save my money toward buying a refurbished iPad or eventually a new iPad. After a week it probably will get easier to ignore the line. But if it drives you crazy you can get a refurbished and maybe sell your old one to somebody who doesn't care very much?
I am assuming your $100 repair is from an independent (unauthorized) shop, because the Apple and Authorized Service Provider cost is listed as $299?
iPad Screen Damage - Official Apple Support
Obviously that's definitely not worth it when Apple is directly selling refurbished units for that price these days.