I would go for decrappify: https://www.fast.ai/2019/05/03/decrappify/

GAN's are hard to train for a new ML practitioner, VAE can have blurry results if you are not using skip-connections like in U-NET.

It sounds like you have training examples (images pre and post processing), but would benefit from an approach using transfer learning since you don't have that many.

Good luck!