You might have heard that the stock market is overpriced after years of solid gains. And it is. That doesn't mean every stock is overpriced, though.

Actually, several biotech stocks look attractively valued right now. Here's why AbbVie (NYSE:ABBV), Celgene (NASDAQ:CELG), and Corcept Therapeutics (NASDAQ:CORT) are bargain biotech stocks you can buy today.

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AbbVie

AbbVie shares currently trade at 13.5 times expected earnings. But if you factor in the big biotech's growth prospects, its valuation appears even more compelling.

The consensus among Wall Street analysts is that AbbVie will grow earnings by an average annual rate of close to 14% over the next five years. I think AbbVie will be able to achieve that level of growth, thanks to a handful of current blockbusters and soon-to-be blockbusters plus a drug pipeline that's ranked third in the biopharmaceutical industry.

AbbVie's fortunes are largely hitched to Humira, the top-selling drug in the world. Sales for the autoimmune disease drug continue to grow. The biotech's fastest-growing star, though, is cancer drug Imbruvica. AbbVie also recently won FDA approval for another product that should become a blockbuster, hepatitis C drug Mavyret. 

Sooner or later, Humira will face challenges from biosimilars. AbbVie thinks its pipeline will prepare it well for that day. The company has high hopes for several candidates, particularly cancer drug Rova-T and autoimmune disease drug upadicitinib.

On top of its low valuation and solid growth prospects, AbbVie also pays one of the best dividends in big pharma. Its yield stands just under 3%. 

Celgene

Celgene's forward earnings multiple of 16 makes it seem a little pricier than AbbVie, but still not too expensive. However, its the biotech's projected earnings growth of 22% annually that really qualifies Celgene as a bargain, giving the stock a price-to-earnings-to-growth (PEG) ratio of 0.90. That indicates a relatively low valuation for a growth stock.

Can Celgene really pull off that kind of growth? I think so. For one thing, the company has been able to post average annual earnings growth of almost 25% over the past few years. Much of that growth was powered by Revlimid -- and Celgene expects continued growth for the blood cancer drug for years to come.

Celgene also has several other products in its current lineup that should fuel growth. Leading the way is autoimmune disease drug Otezla. Pomalyst is another blockbuster in Celgene's quiver. In addition, the biotech claims a near-blockbuster with solid tumor drug Abraxane. 

Then there's Celgene's pipeline. The company believes it will receive approval for 10 current pipeline candidates by 2022 that could generate peak annual sales of $1 billion or more. Four of those drugs could bring in annual sales of $2 billion or more. 

Corcept Therapeutics

Corcept Therapeutics stock might not appear to be a bargain at all, with shares trading at 26 times expected earnings. However, analysts expect the biotech to grow earnings by 73% annually over the next five years. This super-high projected growth rate gives Corcept a PEG of only 0.59 -- definitely in bargain territory.

Of course, Corcept must actually achieve this expected high growth rate, but doing so should be attainable. Sales for Corcept's Cushing's syndrome drug Korlym continue to gain momentum; in the second quarter of 2017, the drug saw sales soar 80% year over year. 

The biotech has an even better treatment for Cushing's disease potentially on the way. Results from a phase 2 study of Corcept's next-generation cortisol modulator, CORT125134, are expected in the first quarter of 2018. A pivotal phase 3 study should follow. The experimental drug appears to offer similar benefits as Korlym but doesn't have the side effects caused by Korlym's affinity for the progesterone receptor. 

CORT125134 could also have potential in treating cancer. Corcept has another phase 2 study underway evaluating a combination of its candidate with Celgene's Abraxane in treating solid tumors. It's even shown promise in treating metabolic disorders such as fatty liver disease and antipsychotic-induced weight gain, with a phase 1 study targeting these indications just starting up. With tremendous opportunities ahead, Corcept appears to be attractively priced right now.

Keith Speights owns shares of AbbVie and Celgene. The Motley Fool owns shares of and recommends Celgene. The Motley Fool has a disclosure policy.