Drennan v. Star Paving

Defendant bid on a job for Plaintiff, which accepted Defendant's bid (it was the cheapest bid). Defendant then said that its bid was a mistake and wasn't supposed to be so low. Plaintiff was forced to seek new bids.

Can Plaintiff seek, as damages, the difference between Defendant's initial winning bid and how much Plaintiff was eventually required to pay?

Yes, Plaintiff is entitled to damages. Defendant's bid is enforceable under promissory estoppel. Defendant had reason to expect Plaintiff to rely on the bid.

You will be bound to a promise if you reasonably expect that the promise will cause the promisee to act in reliance to his detriment, and it actually does cause them to act, if enforcing the promise is necessary to avoid an injustice.