Standup paddle board manufacturer Tower Paddle Boards marketed one of its inflatable boards on Amazon for $549—$250 less than its usual price on Amazon—and the combination blew up sales Monday, giving Tower its best sales day ever.

The manufacturer, which also sells online at TowerPaddleBoards.com, sold nearly 750 boards in 24 hours on Amazon, generating nearly $400,000 in sales. “That’s more than we did in our first year and a half in business,” says founder and CEO Stephan Aarstol.

By comparison, he says Tower sells about $11,000 in merchandise through Amazon’s marketplace on a typical day.

The surge came from marketing the discounted board as an Amazon Deal of the Day, a designation four or five products get each day, which gives those product top placement on the e-retailer’s Today’s Deals page. Today’s Deals is listed in the horizontal navigation bar that appears near the top of every Amazon.com page. Amazon also features a link to Today’s Deals in many of the promotional emails it sends shoppers.

Often products that get “Deal of the Day” billing (which Amazon used to call Gold Box Deals) are shipped and sold by Amazon, but Aarstol says he and Amazon put the offer together as part of Tower Paddle Boards’ participation in Amazon Exclusives. That program showcases products offered by marketplace sellers only on Amazon, meaning the products aren’t available on other mass e-retail sites or in stores.

Participating in Exclusives gets Tower Paddle Boards more marketing and branding support from Amazon. For example, Amazon in January featured Aarstol and Tower Paddle Boards’ small business story in a profile it ran on Amazon’s home-page feature carousel. (Separately, Amazon CEO Jeff Bezos wrote about Aarstol and Tower Paddle Boards’ success on Amazon in his 2015 letter to shareholders.) In exchange for the extra eyeballs on its products, Tower Paddle Boards pays Amazon a 20% commission on each sale, which is 5% more than the company would otherwise pay as an Amazon marketplace seller. Doing the math, this means Amazon collected about $80,000 in commission as a result of Tower’s sales on Monday.

Aarstol says the timing was right for Monday’s sale, as standup paddle boards are coming into their peak season and Tower had the inventory ready. The manufacturer recently arranged a $1 million line of credit with a lender to make sure it had the cash flow to support the additional inventory. Tower also took out loans from Amazon to support sales.

Tower Paddle Boards is working other avenues to get exposure to its products too. It just launched a giveaway contest on Instagram with camera manufacturer GoPro Inc. The contest requires participants to post their best spring or summertime photo on Instagram or Twitter and tag the image with the two companies’ handles—the winner will get a standup board and a camera. The first post about the contest went out on Monday and had 185,000 likes on Instagram by Wednesday. Aarstol says Tower gained about 750 Instagram followers in the first 24 hours as well.

Amazon is No. 1 in the Internet Retailer 2016 Top 500 Guide. GoPro is No. 323. Tower Paddle Boards, which generated about $7.2 million in sales last year, with 44% of that coming through Amazon, will make its debut in the 2016 Second 500 Guide when it is published next month. To learn more about Tower Paddle Boards and its development—which includes appearances on ABC’s Shark Tank and Beyond the Tank TV shows that garnered it investment from billionaire Mark Cuban, see this Internet Retailer story.