If you are looking for a top growth stock to add to your portfolio, scoping out Cathie Wood's ARK Innovation ETF (NYSEMKT:ARKK) can be a great place to start. Focused on disruptive stocks with lots of potential, the fund is home to some of the most promising investments out there. However, the problem is that many of them are expensive, and will cost you a hefty premium to get in on the action.

But that doesn't mean there are no fairly valued companies in the mix. Three cheap stocks to consider from that fund are Regeneron Pharmaceuticals (NASDAQ:REGN)Baidu (NASDAQ:BIDU), and Paccar (NASDAQ:PCAR). With relatively low valuations and tons of potential, these are among the best Cathie Wood stocks to buy today.

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1. Regeneron

Healthcare company Regeneron rallied last week after it released data from a phase 3 trial of its antibody cocktail REGEN-COV. The results showed that the treatment was 81% effective in reducing the risk of symptomatic COVID-19 infections. And for those people who took the cocktail and did develop symptoms, they recovered in just one week versus three weeks for those who received the placebo.

It's a great result for Regeneron, and suggests that people could take the cocktail as a preventative measure if they are concerned about contracting COVID-19 (such as those living in the same household as someone who tested positive, which is what the trial focused on).

Given that the coronavirus still remains a threat in countries all over the world, these results could generate significant demand for Regeneron's antibody cocktail. The U.S. Food and Drug Administration (FDA) previously issued an emergency use authorization (EUA) for the treatment in November 2020 for people with mild to moderate cases of COVID-19. Regeneron says it will ask the FDA to expand that authorization to also cover preventative measures for appropriate populations.

Regeneron is already a promising growth stock, even without taking its COVID-19 treatment into account. When it last reported quarterly earnings on Feb. 5, its fourth-quarter sales for the period ending Dec. 31, 2020 totaled $2.4 billion and grew by 30% year over year. That includes 10% sales growth from one of its main products, Eylea, which treats vision loss.

The company currently has 20 trials ongoing that are either in phase 2 or later, so it isn't running out of growth opportunities anytime soon. With so much going on, it is surprising that shares of Regeneron are down 11% in the past year while the S&P 500 has soared by 44%. At a forward price-to-earnings (P/E) ratio of just 10, the stock is a bargain, especially compared to Eli Lilly (another company that has an EUA for a COVID-19 treatment), which trades at more than 23 times its future earnings. Regeneron looks like a winner, and while its trading at a cheap price, it could generate especially great returns for your portfolio.

2. Baidu

Baidu trades at a higher forward P/E than Regeneron, but at 20, it's still cheap for a tech stock. It offers similar services to Alphabet's Google, like a search engine and video sharing, but focuses on the Chinese market. Alphabet, however, trades at 33 times its future earnings. And Baidu's relatively low ratio is despite China presenting some more attractive growth opportunities right now. The country is coming off an impressive first quarter during which its economy grew by 18.3%. According to estimates from GDPNow, the U.S. economy is on track to grow 10 points lower, at a much more modest rate of 8.3%.

Although it may not be likely for China to continue growing at such high rates, with the country having control of COVID-19 and already showing strong results, investors shouldn't ignore the potential that market possesses. Adding some exposure to China can create some great diversification.

For the last three months of 2020, Baidu generated $4.6 billion in revenue and grew by 5% from the prior-year period. And for the first quarter of 2021, the company projects sales potentially rising as high as 26% year over year to $4.4 billion. However, it's important to note that the growth rate for Q1 will be inflated due to the pandemic, as the first three months of 2020 were impacted by the coronavirus beginning to heavily impact global economies.

Even though Baidu's stock has more than doubled in the past year, with lots of growth on the horizon this is still an investment that could go much higher in the near future.

3. Paccar

Paccar is a heavy-duty truck manufacturer with a future-minded focus on the autonomous and electric vehicle markets. Earlier this year, Paccar announced a strategic partnership with self-driving company, Aurora. Two of Paccar's trucks, the Kenworth T680 and Peterbilt 579, are already using Aurora Driver technology. Those versions could be "delivered in the next several years." Fortune Business Insights projects that the autonomous trucks market will be worth more than $2 billion in 2027, rising at a compound annual growth rate of 12.6% until then.

Tesla has also gotten involved in producing trucks. It's arguably the hottest self-driving stock out there, rising around 400% in the past 12 months, while Paccar is up by 43% during that time frame. But in terms of valuation, Tesla's share price is incredibly steep. Investors are getting more bang for their buck with Paccar, which trades at a forward P/E of 16 compared to Tesla's multiple of more than 173. While Tesla only recently achieved profitability in 2020, Paccar has recorded a profit for 82 years in a row.

Although the pandemic has hurt sales with the company's top line of $18.7 billion in 2020 declining 26.8% from the previous year, there is still tremendous potential over the long term. With a modest valuation, this is another top growth stock that is underrated right now.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.