On the store main page, it shows Fallout collection picture and says 2.49 dollars. Yet, the price at checkout is 4.99... If you click on the add to cart button on the main page, it adds Fallout 2 only. Seems like false advertising to me. 

 
I see price mistakes on a lot of different websites. Seem to just be a fact of life these days. I've seen a keyboard advertised for $70.00 once, and at check out, the price went up to $70,000. Fortunately, I didn't buy it. I didn't sue them either.          ;)

I'm pretty sure to make a false advertising claim you have to fully influence a purchase under false pretenses. Because they fully alert you to what you are buying before you purchase, though it may seem devious, they aren't explicitly selling you something different than what they advertised. They may be preying on those who don't pay attention, but that's not against the law last I checked. 

Happens occasionally on Steam, they usually sort it out after a little while.