Shake Shack stock hasn't been this cheap in years. Stifel says it's time to buy

Shake Shack is trading at a discount investors can't ignore following an earnings-driven sell-off, according to Stifel. The investment firm upgraded the fast casual chain to buy from hold. It lowered its price target to $85 from $105, but that still implies 23% upside from Thursday's close. Shares tumbled 28% on Thursday after the company said it broke even for the first quarter on a per-share basis. Analysts polled by FactSet expect a profit of 12 cents per share. …