Having yt-dlp save the videos to S3 will just add to your costs - what benefit will it provide to your users to get the file from S3 compared to Youtube?
While ‘cloud computing’ is managing servers in the cloud like EC2, they’re still just servers like you’d run in your lab. To do it the ‘cloud way’, use the cloud services instead.
My suggestion would be a price checker - create a webpage maybe with S3 or Lightsail where users can enter in a URL for a product, an email address and a scrape recurrence time like 24hours, then have Lambda scrape the page & email the price to the user on that schedule. Use DynamoDB (or a relational DB like Postgresql) to save the results, schedule, etc.
Try not to use EC2 at all if possible. Or instead of EC2, use EKS if scraping with Lambda is too difficult.
The most important thing is getting the security right, from your access to AWS to ensuring your database isn’t easily downloaded by just anyone.
That’s a bad take, there will always be people who will say we can never afford it. The real question should be ‘can we afford not to’ as people live and die in miserable conditions.