I have a generic padded neoprene zippered case I bought from Amazon for less than $20 years ago. I've used if for every model Mac portable I've had since them. I can't imagine needing to spend more than that. I only use mine if I'm putting the laptop in a bag that doesn't have a builtin laptop pocket.
I ordered it so long ago I can't even find it in my Amazon history (or maybe I bought it somewhere else). But, it looks a lot like this:
Neoprene Case
You've given no indication on what you need a case for so it would be really hard for someone to make a specific recommendation. The only thing that really matters is the size of your computer, not the model or the internal configuration. Search Amazon (or your preferred vendor) for cases for a 15" laptop and find one that you like.