Buy one pan or a whole set?

So lately I've been having fun and games with my cooking, food sticking to the pan even though it's non-stick so it's kind of old obviously and it's crowned in the middle.

So I'm kind of debating buying a new set or should I just buy one or two pans and maybe 20 bucks for them, or go out and spend the $50 to buy a big set?

(I'll go Sunday morning to shop)