A customer has a website which shows all the deals available across the market. The site experiences a load of 5 large EC2 instances generally. However, a week ...

A customer has a website which shows all the deals available across the market. The site experiences a load of 5 large EC2 instances generally.
However, a week before Thanksgiving vacation they encounter a load of almost 20 large instances. The load during that period varies over the day based on the office timings.
Which of the below mentioned solutions is cost effective as well as help the website achieve better performance?