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Photo: Flickr user Pictures of Money.

When I started investing, I bought only stocks that traded for less than $5. I figured it wouldn't take much for the share price to double or more, and I'd get rich fast. I soon learned the hard way that the price tag on a single share tells you nothing about the quality of the company behind the stock.

Yet many investors won't buy stocks that trade in the triple digits, because they think the price won't be able to move any higher. The logic is flawed for the same reason my single-digit-stock logic was. Stocks can always move higher.

With that in mind, here are three biotech companies with stock prices over $100 that I think are worth every penny.

1. Gilead Sciences (NASDAQ:GILD)
Gilead has been a dream stock for years, and its share price drove past the $100 mark last year, but don't let that scare you off. This stock offers biotech investors an investing trifecta of growth, value, and income. 

Gilead commands a market-leading position in two huge disease states, HIV/AIDS and hepatitis C, and it makes a mint from several best-selling medicines to treat them. Harvoni, Sovaldi, Truvada, and Stribild are all growing cash cows, contributing billions to the company's top and bottom lines and helping to keep the company's revenue diversified and growing.

Gilead also boasts an enviable pipeline, with dozens of compounds being tested in 36 clinical trails, many of them in phase 3 or already pending regulatory approval. Given its history of successfully navigating the regulatory process, the odds are good that at least a few of these compounds will one day turn into blockbusters.

While we wait for that to happen, Gilead is using its huge financial resources to reward its investors: The stock pays a dividend that yields around 1.5%, and the company has authorized a massive $15 billion share-repurchase program. Considering that Gilead's stock currently trades for less than 12 times trailing earnings and that analysts are projecting profits to grow around 16% per year for the next five years, Gilead seems like a bargain to me. 

2. Celgene (NASDAQ:CELG)
Like Gilead's, Celgene's stock is currently trading for over a little over $100, and for good reason. The company has several drugs that are growing quickly, including its cash-gushing multiple myeloma therapy Revlimid, which rang up more than $1.4 billion in revenue and grew an impressive 19% in the past quarter alone.

Beyond Revlimid, Celgene has two other drugs that could reach blockbuster status this year: Pomalyst, which also treats multiple myeloma, and Abraxane, which is approved to treat breast, lung, and pancreatic cancer. When these are combined with the company's other drugs, management expects to bring in more than $9 billion in sales this year, up sharply from $7.6 billion last year. Better yet, management believes that earnings per share will surpass $4.75 in 2015. Even though the stock trades north of $100, that means shares can be purchased for around 26 times 2015 earnings. For a high-quality company like Celgene, I think that's a perfectly fair price, and it could even be considered cheap if the company hits its 2020 EPS target of more than $13 per share.

3. Alexion Pharmaceuticals (NASDAQ:ALXN)
While Alexion is quite a bit smaller and not as well known as Celgene and Gilead, it fetches a higher share price than either. A single share will currently set you back about $168.

The company's high share price owes largely to the success of a single approved drug, Soliris, which treats two ultra-rare, life-threatening blood disorders: paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. Despite having just one approved drug, this company has seen its stock go on an amazing run for years.

More recently, the company announced two regulatory wins for drugs that fit nicely into its playbook of focusing on ultra-rare diseases. These two new drugs, Kanuma and Strensiq, have been cleared for sale in Europe and are both currently pending FDA approval in the United States. Each holds blockbuster potential.

At 57 times trailing earnings, Alexion's stock is the most expensive of the group, but given the catalysts of these two new drug launches in Europe and the likelihood of upcoming FDA approvals, Alexion still has years of strong growth ahead of it, and it could make a fine addition to the more speculative side of your portfolio.

Brian Feroldi owns shares of Gilead Sciences. The Motley Fool owns and recommends Celgene and Gilead Sciences. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.