Theoretically, a stock's price shouldn't matter. While it's true that a stock's performance should be relatively in line with the company's, ultimately, the dollar value of a share is a function of both the company's underlying results and how many shares have been issued. That second factor can give a high market-cap company a lower stock price than a smaller one.

Still, there's just something compelling about scooping up low-priced shares. Not only is it easier to buy a round-number lot when investing in inexpensive stocks, there's some evidence to support the idea that they actually tend to outperform their higher-priced counterparts.

To that end, here are three great sub-$10 stocks that could spice up your portfolio.

Man's hand offering a $10 bill from his stack of paper money

Image source: Getty Images.

Sirius XM Holdings has staying power

In this day and age of mobile broadband, it seems rather amazing that a hardware-specific, subscription-based satellite radio business can thrive. But, Sirius XM Holdings (NASDAQ:SIRI) is doing exactly that. In 2019, for its tenth consecutive year, it added more than 1 million paying members to bring its total subscriber base to almost 30 million. The company's revenue growth has been just as reliable for longer.

It's growth pace is slowing, admittedly. As my fellow fool Rick Munarriz pointed out earlier this year, 2020's top line is expected to only improve by 4%. Each year that passes brings the satellite radio stalwart closer to full penetration of its total addressable market.

What Sirius XM lacks in additional growth potential, however, it makes up for in consistency. See, its customers aren't devoted to commercial-free mobile radio. They're devoted to the personalities behind their favorite programs, and they're willing to keep paying for ongoing access to shows done by the likes of Howard Stern. Sirius also offers access to sports events and programs that may not be available any other way, like "Aussie Football Rules America with Eddie McGuire."

And Sirius XM has something in the works for a second act, once satellite radio reaches its full potential. This month, it acquired Simplecast, which will help it better monetize its existing podcast business.

Sirius XM (SIRI) revenue and per-share earnings, past and projected

Data source: Thomson Reuters/Refinitiv. Chart by author.

Not the Nokia you think you know

Most consumers will mentally categorize Nokia (NYSE:NOK) as a mobile phone maker, and to be fair, it's still in that business even though it sold a big chunk of its smartphone division to Microsoft back in 2013. It's not a power player in the arena, but its mobile devices still take a small piece of wireless phone market.

Phones themselves are less and less of a priority for the company though. The burgeoning opportunity in front of Nokia -- one that many investors have yet to fully appreciate -- is 5G.

You read that right. Nokia is a 5G play. It's potential may not be on par with that of Ericsson or Qualcomm, but it's scoring its victories here and there. In mid-June, for instance, it announced that China Unicom (NYSE:CHU) had tapped it to supply about one-tenth of the tech for its planned 5G network. Around that same time, it became the first wireless broadband technology name to produce 1 GB wireless broadband speeds in the United States using C-band frequencies that had previously been unavailable to mobile network operators and manufacturers. That's a huge deal given how crowded the country's radio waves have gotten.

It will take time for the company's wins to bear fruit, but at less than $5 per share for its U.S.-traded American depository receipt (ADR), this tech company may be worth the wait.

Nokia (NOK) quarterly revenue and per-share earnings, historical and estimated

Data source: Thomson Reuters/Refinitiv. Chart by author;.

Plug Power is coming of age

Finally, add Plug Power (NASDAQ:PLUG) to your list of stocks priced under $10 to consider -- it's presently trading around $6.80 per share. It's not exactly a household name, but the number of households familiar with the it is on the rise, as is its revenue. Its march toward profitability is underway as well.

The underpinnings of that progress are rooted in the gradual growth of interest in what the company does. Plug Power's tech, in simplest terms, converts stored hydrogen into electricity. That not only makes for great backup power systems, but more and more, it's proving itself as a viable primary option for the generation of electricity. Last year, Plug Power's top line grew nearly 40%, reflecting improving customer awareness.

If the upcoming semitrailer from Nikola works as well as CEO Trevor Martin has asserted, hydrogen fuel cells as a power source for vehicles of all sizes will be validated; Plug Power makes those too.

Perhaps the most compelling aspect of an investment in Plug power, however, is how rapidly its approaching financial viability. At its present pace, the company could swing to a profit sometime in 2023. The market should reward progress toward that finish line in the meantime.

Plug Power (PLUG) quarterly revenue and per-share earnings, historical and estimated

Data source: Thomson Reuters/Refinitiv. Chart by author.