You've heard it before: It takes money to make money. However, that doesn't mean that you must have a lot of money to invest upfront to generate sizzling returns.
There are stocks you can buy with relatively modest initial investments that can pay off big-time over the long run -- and sometimes, even in the short run. If you've got $2,000 to invest now, here are three unstoppable stocks that have the potential to more than double your money pretty quickly.

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Ayr Wellness
Marijuana stocks are hot right now -- especially those of U.S.-based companies. Multistate cannabis operator Ayr Wellness (AYRW.F 0.58%) is a great example. Its shares skyrocketed more than 150% last year and are up by close to 35% so far in 2021.
There's a good reason for that impressive performance. Ayr's revenue and adjusted earnings before interest, taxes, depreciation, and amortization (EBITDA) continue to grow robustly. This growth has come from the company's operations in Nevada and Massachusetts. But Ayr is already expanding beyond these markets.
The company is poised to enter Arizona, which just launched its adult-use cannabis market. It will also soon enter the fast-growing medical cannabis markets in Florida, Ohio, and Pennsylvania via strategic acquisitions.
Compared to most multistate operators, Ayr is dirt cheap. Its shares trade at less than six times sales -- well below its peers. This valuation combined with its strong growth arguably puts Ayr in the best position of any U.S. pot stock to double or more in the not-too-distant future.
Gore Holdings VI
Special purpose acquisition companies (SPACs) are popping up nearly everywhere you look. Gore Holdings VI (GHVI) appears to be one of the best. It's set to merge with Matterport in the second quarter.
Matterport reigns as the leader in spatial data. The company's technology can map any physical space -- homes, offices, museums, you name it -- into a 3D digital model. So far, virtual 3D "twins" of more than 10 billion square feet of space have been created.
There are lots of reasons for digitizing physical spaces. 3D models help improve design, construction, maintenance, and especially marketing. Matterport primarily relies on a software-as-a-service model where it receives recurring revenue for providing customers with access to their spatial data and tools to make smart use of it.
It's not surprising that Matterport's subscriber base skyrocketed by more than 500% last year; it now includes more than 13% of the Fortune 1,000. The company estimates its total addressable market at $240 billion. With Gore Holdings VI's market cap currently below $750 million, Matterport will only have to capture a sliver of that potential market to more than double in value.
TransMedics Group
You're probably aware that organs for use in transplants are in high demand. But did you know that only two to three out of every 10 hearts and livers from donors are actually used? The limitations of current cold-storage solutions are one culprit. TransMedics Group (TMDX 1.68%) has an answer to this problem.
The company developed its Organ Care System (OCS) for hearts, lungs, and livers. The systems mimic many aspects of organs' functioning environment within the body. OCS improves the utilization rate of donors' organs. It also decreases the risks of post-transplant complications.
TransMedics has already received FDA approval for its OCS Lung product. It hopes to gain approval for its heart and liver systems this year; an FDA advisory committee is scheduled to review the company's heart system on April 6. A positive decision would likely provide a major catalyst for TransMedics, making this a stock you'll probably want to check out sooner rather than later.
The company thinks that the total addressable market for its lung, heart, and liver systems is close to $8 billion annually. TransMedics' market cap is currently only a little over $900 million, so its stock could do a lot more than double if all goes well with the FDA decisions on the way.