While Frontier Airlines seems to have some sort of sale every.single.day, their 99% sale is back for a one-day only Black Friday special. Just use promotion code SAVE99 to get the discount. This is for travel for the following days: Nov. 28-30, 2018; Dec. 1, 4-5, 8, 11-15, 17, 19, 2018; Jan. 8-16, 19-20, 23-26, 28-31, 2019; Feb. 2, 5-7, 2019. Between this sale and the Spirit sale, you are bound to find some cheap flight if you are flexible!
This promotion is valid for nonstop domestic travel and unfortunately there are many routes that are not eligible or do not even fly on those particular days. While the dates and route exclusions can be limiting, there are definitely some amazing deals to be found. You can also check out all of their nonstop routes here.
Remember though, with Frontier, you are charged for every little extra thing, including seat assignment and cary on bags. So even though this might turn out to be a great deal, with all the ad-on fees, make sure it truly is a deal for you!