There's no authentic Japanese restaurant in Kuwait simply because it's inedible for most.
Price wise, they are mostly priced the same. In all cases they have makis and sushis that are priced 2.500 KD and priced at 7.000 KD. It's all about what you're selecting and what the ingredients are.
I think Sakura does all you can eat sushi, not sure if they still do that.
Also there are cheaper options on Talabat, so you might want to look where those places are located (if they have a restaurant)