Join Frontier's Discount Den, get a $50 flight voucher and access to Kids Fly Free

Frontier, the Denver-based discount airline, is running a promotion this week for its Discount Den membership. Through December 30, when you purchase a membership ($60 per year) you'll receive a $50 flight voucher. The voucher will be emailed to you on January 2 and must be used Mar. 30.

The main drawback of low-cost carriers is the fees that get tacked on for everything from seat selection to carry-on bags. With a Discount Den membership you won't save on ancillary fees, but you (and up to six people traveling with you) will have access to Frontier's cheapest fares. The discount varies depending on the flight, but most often you'll save $10 each way.

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Frontier maintains a consistently updated flight sales page and, at times, the best deals are only available to Discount Den members. It's common to see one-way flights for as little as $15-$20.

But for families, the best feature of a Discount Den membership is the Kids Fly Free promo. With Kids Fly Free one child (under 15 years old) can fly free with each adult ticket, but there are restrictions. Only flights on the days listed below are available for the promotion. And there are blackout dates and certain markets that are excluded.

Summer Hull, head of TPG Family, was able to save more than double the cost of a membership on her first flight thanks to the Kids Fly Free promotion.

This promotion has been extended and modified since it's introduction. Currently, the Kids Fly Free deal is only valid on domestic round-trip travel through Aug. 8, but you'll need to book the flight by Jan. 8. Also, a 14-day advance purchase is required. You can see the program's up-to-date terms here.