How much money does one need to start investing in stocks? $1 million? $10,000? The truth is, even a relatively modest sum of $100 is enough to get started for two reasons. First, nowadays, it isn't hard to find online brokers that offer fractional shares. Second, there are excellent companies whose shares are trading for far less than $100 apiece.

Let's consider two stocks you can afford with less than $100 today: Pfizer (PFE 0.55%) and Doximity (DOCS 0.97%).

1. Pfizer

Pfizer can't catch a break. The company has been dealing all year long with a steep decline in sales from its coronavirus vaccine Comirnaty, and COVID therapy Paxlovid. The drugmaker's total revenue dropped off a cliff as a result. And more recently, Pfizer disappointed investors with its guidance for 2024. Needless to say, Pfizer stock isn't considered a hot commodity right now.

But it should be, at least for investors looking well beyond next year. Pfizer has substantially expanded its lineup this year with a historic string of brand-new approvals. The company has also relied on acquisitions to help. For instance, it dished out $43 billion in cash to buy out cancer specialist Seagen.

A corporation can do that when sitting on tons of cash, which Pfizer was due to its success in the coronavirus market. That's the important thing to keep in mind. If it hadn't been for Pfizer hitting gold by marketing Paxlovid and Comirnaty, the company would still have somewhat similar issues, only with less money and less preparation to deal with them.

But the steps the company took in the past couple of years have helped ensure that it will have an incredibly deep pipeline that could deliver important new medicines down the line, in addition to the ones it is already launching this year. The drugmaker is a solid dividend stock, too, yielding nearly 6% right now.

For all those reasons (and more), Pfizer remains an excellent stock to buy for long-term investors, and the company's shares are changing hands for just $27.22 apiece as of this writing. Investors can easily afford three shares with plenty of cash left on the initial $100 capital to spare.

2. Doximity

Doximity is a professional networking platform that focuses on medical workers. It offers a range of perks, from communication between doctors to reading up on the latest research in one's field, telemedicine visits with patients, and more.

However, Doximity has also failed to keep pace with the broader market this year because its financial results are not as strong as they once were. For instance, in the second quarter of its fiscal 2024, ended on Sept. 30, Doximity revenue grew by just 11% year over year $113.6 million. That compares unfavorably to the top-line growth rates investors are used to in the past.

DOCS Revenue (Quarterly YoY Growth) Chart

DOCS Revenue (Quarterly YoY Growth) data by YCharts

Still, there are many things to like about Doximity's business. First, the company is already profitable. It reported an adjusted net income of $45.6 million in its latest period, an increase of 26% year over year. Second, Doximity typically reports excellent margins. The company's adjusted net profit margin came in at 40.1%, compared to 35.4% in the year-ago period. Third, Doximity benefits from a solid competitive advantage in the form of the network effect.

It has already attracted more than 80% of physicians and more than 90% of graduating medical students in the U.S. On top of that, the 20 largest pharmaceutical companies and the 20 largest health systems all use the platform to interact directly with physicians, be it to post job offers or advertise results from clinical trials for medicines.This deep ecosystem ensures that in the future, more physicians -- and companies looking to communicate with them -- will join the platform.

Lastly, Doximity still sees a long runway for growth ahead. The company estimates a total addressable market of $18.5 billion. Its trailing 12-month revenue is far less than 10% of that at $448 million. Meanwhile, Doximity's shares are just $27 each right now. Investors who get in now at these levels could be handsomely rewarded.