Research shows that 70% of millennials are not invested in the stock market, despite its proven ability to create wealth over long periods of time. One of the most common reasons millennials sit on the sidelines is the misconception that they need more money to get started.

That logic fails to consider the profound impact of compounding. Money invested today can start growing, and it can build on itself as time passes. So the most prudent course of action is to start putting money into the stock market as soon as possible, no matter how small the sum.

With that in mind, Palantir Technologies (PLTR 3.73%) and Adyen (ADYE.Y -1.57%) have compelling growth prospects that make current valuations appear reasonable, and both stocks are widely accessible at less than $20 per share.

Read on to learn more about Palantir and Adyen.

1. Palantir Technologies

Palantir is a data science company with a unique history. Its first platform was built to assist customers in the defense and intelligence community with counterterrorism operations. Palantir has since expanded into the commercial sector, but its products are still designed for complex, high-value use cases, according to Forrester Research.

Palantir provides software that integrates information and machine learning (ML) models to form an ontology, a map that links related data points.

For instance, flight numbers could be linked to airplanes, airports, and destinations. Users can surface ontology data with various analytics tools and artificial intelligence (AI) applications. In this example, flight numbers could be organized into schedules to optimize arrivals and departures.

Palantir helps businesses use AI in a way that creates real value, and it does so to great effect. Forrester Research has recognized the company as a leader in AI/ML platforms, and Dresner Advisory Services has recognized its leadership in model operations, a discipline that deals with model lifecycle management across development, evaluation, and optimization.

Palantir reported encouraging results in the third quarter. Its customer count rose 34% to 453, revenue increased 17% to $558 million, and GAAP net income was $72 million, marking its fourth consecutive quarter of GAAP profitability. Sales growth was especially strong among commercial clients, something management attributed to its AIP (Artificial Intelligence Platform).

AIP launched earlier this year, bringing support for large language models and generative AI applications to existing Palantir platforms. Management sees the product as a game changer. To quote Chief Revenue Officer Ryan Taylor, "The potential market for AIP and the trajectory of possible AIP growth for our business is massive."

Going forward, Morgan Stanley believes Palantir could grow revenue at 30% annually through 2029, and Dan Ives of Wedbush Securities sees the company as the "gold standard in AI." In that context, its current valuation of 19 times sales appears tolerable, though it is a slight premium to the three-year average of 18.8 times sales.

Patient investors that can handle volatility should feel comfortable buying a few shares of this growth stock today.

2. Adyen

European fintech Adyen simplifies electronic payments for businesses. Its full-stack platform integrates gateway, processing, and acquiring services across online and offline channels. That means Adyen handles various tasks from transaction authentication and authorization to the settlement and deposition of funds in merchant accounts.

The company also provides embedded financial services for marketplaces, such as the ability to create accounts, issue payment cards, and send payouts.

By unifying those capabilities on one platform, Adyen creates value for businesses in two ways.

First, it eliminates complex integrations and fees charged by the unnecessary intermediaries (often north of 10) involved in payment processing. Second, Adyen can optimize authorization rates, prevent fraud, and surface insights for merchants by applying machine learning to the robust data it captures from across the payments value chain.

That value proposition is resonating with the market, as evidenced by the major brands that partnered with Adyen. It clients include marketplaces like Etsy and eBay, digital businesses like Spotify and Uber, food and beverage brands like Domino's Pizza and McDonald's, and retailers like Gap and Levi Strauss.

Adyen stock dropped 40% following the release of its first-half financial report. Net revenue rose 21% to 739 million euros, a steep shortfall to the 40% growth forecasted by analysts. Worse yet, IFRS net income remained flat at 282 million euros due to aggressive headcount expansion.

However, those weak results are due to difficult economic conditions, not Adyen falling out of favor with merchants. I say that because volume churn was below 1% through the first half of the year, meaning customers are sticking around. Assuming that continues, Adyen has a good shot at reaccelerating growth when economic conditions improve.

Indeed, management expects net revenue to grow in the low-20% to high-20% range through 2026. Similarly, Morningstar analysts think Adyen can grow net revenue at 22% annually over the next five years, and 16% annually over the next decade.

That forecast makes its current valuation of 6.7 times sales look quite attractive, especially when the three-year average is 9.8 times sales. Investors should start with a small position in this growth stock.