I'm afraid there is no fast solution in order to change the price in 2 seconds using Shopify. But we have our own app, which is very popular in Sales section of Apps Store.
It's called Bulk Discounts & Sales Scheduler and allows you to set up discounts for products in a few clicks with a bulk discounts tool and switch between prices.
Schedule sales for holidays, Black Friday, Cyber Monday, any sales.
Add special Sale labels to products with discounts and make them more perceivable.
Recently, we released a new discount app that applies discounts for thousands of products in a few seconds. Now it possible to switch between sale and normal prices in 5 seconds :)
I know the thread is old but I recently developed an app for this purpose: "Ahia! - Easy Price Changer".
You can find it here: https://apps.shopify.com/ahia-easy-price-changer
You can do a lot of things with it:
A lot of new features are being developed and will be released soon.