Many investors distinguish between two kinds of stocks: growth stocks and value stocks. Growth stocks tend to be expensive, but have lots of room to expand their businesses and grow their earnings. Value stocks tend to be more mature companies. They aren't expected to grow much, but they can sometimes be found at a very cheap price.

But what if you could get the upside potential of a true growth stock at the cheap price of a value stock? Then you would have a super stock! Opportunities like that don't come around often -- but Spirit Airlines (NASDAQ:SAVE) just might be one.

Strong profitability
First, let's take a look at Spirit Airlines' enviable profitability. In 2014, it produced an adjusted pre-tax margin of 19.2%, among the best in the history of the U.S. airline industry.

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Spirit Airlines is one of the most profitable airlines in the world. Image source: Spirit Airlines

Investors have panicked this year about a steep decline in Spirit's average fare. Yet the company is on pace to earn an even higher profit margin in 2015, as fuel prices have plummeted. Spirit has projected that its operating margin will be in the 21.5% to 23% range for the full year.

Depending on fuel price trends and how the industry fare environment develops next year, it's possible that Spirit's earnings will fall modestly in 2016. American Airlines (NASDAQ:AAL) has started to aggressively match Spirit's low prices, putting pressure on its fares. But Spirit's average fare is already on pace to drop below $60 this quarter -- it's not likely to go much lower.

Even with this fare war going on, analysts expect Spirit to earn more money in 2016 than the record profit it produced in 2014. In the long term, its industry-leading cost structure means that it should be able to remain profitable in good times and bad. In bad times, higher-cost carriers like American Airlines will run into trouble and start cutting back their capacity well before Spirit Airlines would have to.

Huge growth potential
Next, let's look at Spirit Airlines' massive growth opportunities. The company ended last quarter with 76 airplanes. That makes it one of the smaller commercial airlines in the U.S. By contrast, American Airlines has nearly 1,000 planes in its mainline fleet.

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Spirit is still quite small compared to megacarriers like American Airlines. Image source: American Airlines

Spirit Airlines has firm plans to grow its fleet to 145 planes by the end of 2021. However, that's a very conservative estimate, as Spirit intends to increase its capacity by 15% to 20% annually for the foreseeable future. If it grows its fleet just 15% annually, it would end 2021 with about 185 planes -- more than twice as many as it has today.

There will be plenty of opportunities for growth beyond that. Spirit Airlines' management has stated that the company could potentially earn a 15% or higher profit margin on any route in the U.S. with more than 200 daily passengers. Hundreds of routes fit that description. Even in 2025, Spirit Airlines will have ample room left for growth.

Cheap valuation
The average U.S. stock trades for about 17 times forward earnings. Spirit Airlines clearly has a lot more growth potential than the average company. Yet its stock has lost more than half of its value in the past year, and now trades for less than 10 times earnings.

As Spirit Airlines executes its growth plan for the next decade and beyond, its earnings per share should skyrocket. EPS could quite plausibly quadruple or quintuple in that timeframe. If so, this beaten-down stock isn't likely to stay cheap for very long. Buying Spirit Airlines shares today and holding them until 2025 -- or longer -- could therefore be the first step to building long-term wealth.

Adam Levine-Weinberg owns shares of Spirit Airlines and is long March 2016 $40 calls on Spirit Airlines, long June 2016 $30 calls on Spirit Airlines, and long January 2017 $30 calls on American Airlines Group. The Motley Fool is long January 2017 $35 calls on American Airlines Group. The Motley Fool recommends Spirit Airlines. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.