I wouldn't call five guys cheap, but it's also not super expensive either. At least where I live, a burger, fries, and drink from five guys costs about the same as a quarter pounder, large fry, and drink from mcdonalds.
pretty good deal all things considered, especially cus a small fry from five guys is way more than a large fry at mcdonalds. also you can ask for extra fries and they'll usually fill up a brown paper bag with fries and not charge you more.
as for the most overpriced fast food? that's definitely jimmy johns. $10 for just a cold sub with mayo and iceberg lettuce? no thanks.