There are a lot of stocks that are much cheaper than they've been in a while. That doesn't necessarily make them cheap, though. Think about it this way: Someone could cut the price of a pet rock from $10,000 to $5,000, but it still wouldn't be a bargain. 

However, there are some stocks that really do appear to be inexpensive right now. Three in the healthcare sector that stand out are Alexion Pharmaceuticals (NASDAQ:ALXN), Cigna (NYSE:CI), and HCA Healthcare (NYSE:HCA). But should you buy these dirt-cheap stocks?

A man scratching his head while staring at drawings of question marks and money bags on the wall in front of him

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1. Alexion Pharmaceuticals

Alexion's shares currently trade at around 7.5 times expected earnings. Its price-to-earnings-to-growth (PEG) ratio is a really low 0.57. Any stock with a PEG below 1.0 is generally viewed as attractively priced. You won't find too many stocks with as low of a valuation that also delivered 20% revenue growth last year along with astronomical earnings growth. 

There's a reason Alexion's shares are so inexpensive, though. Nearly 80% of the biotech's total product sales come from one drug: Soliris. And while the drug has been a runaway success for Alexion, its perch at the top could be threatened.

It's unknown how much longer Soliris will enjoy patent exclusivity. Alexion is appealing the revoking of a key European patent for the drug. One key U.S. patent expires in 2021, although the company has other patents that go through 2027. In addition, Apellis Pharmaceuticals reported positive late-stage results earlier this year for pegcetacoplan, which beat Soliris in a head-to-head matchup in treating rare blood disorder paroxysmal nocturnal hemoglobinuria (PNH) -- an important indication for Soliris.

However, Alexion has its own replacement for Soliris that's picking up significant momentum with Ultomiris. The company's acquisition of Achillion gives it a promising Factor D program. Wall Street analysts project that Alexion's earnings will grow by 13% annually over the next five years, slower than in the past, but still solid. My view is that Alexion is a biotech stock worth buying at its discounted price.

2. Cigna

Cigna appears to be the most attractively priced health insurance stock on the market right now. Its stock trades at less than 10 times expected earnings with a PEG ratio of 0.85. 

It's not surprising that Cigna's shares have been clobbered more than the S&P 500 index during the market crash. The company's bottom line could take a hit if the coronavirus pandemic causes medical costs to rise significantly, which could very well happen with large numbers of COVID-19 cases in the U.S.

Most of Cigna's year-over-year growth in the fourth quarter stemmed from its acquisition of pharmacy benefits manager Express Scripts. However, the company's core insurance businesses also performed well thanks to gaining additional members and premium increases.

The existential threat that Medicare for All proposals might have presented for Cigna seems to have practically evaporated with former Vice President Joe Biden's commanding lead in delegates for the Democratic presidential nomination. However, health insurers could still come under fire regardless of who sits in the Oval Office beginning in 2021. Although Cigna is dirt-cheap right now, my view is that there are better stocks to buy with fewer potential headwinds.

3. HCA Healthcare

HCA Healthcare's shares have been hammered harder than any of these three stocks. But this shellacking has made the hospital operator look really inexpensive, with shares trading at less than nine times expected earnings. HCA's PEG ratio stands at 0.91.

Hospitals across the U.S. are already feeling a major impact from COVID-19. It will almost certainly get much worse before it gets better. The coronavirus pandemic is also causing hospitals to postpone elective surgeries that are often relatively lucrative.

As the nation's largest hospital operator, HCA could be affected more heavily by the coronavirus outbreak than its smaller peers. However, the company could also have help on the way. A major stimulus bill that would steer billions of dollars to hospitals seems likely to pass in both houses of the U.S. Congress and be signed into law by President Trump.

Is this beaten-down hospital stock a bargain worth buying right now? I normally wouldn't be a fan of HCA Healthcare as an investment, but we're in a period that isn't normal, to say the least. I think the stock will bounce back once the crisis is over and should deliver tremendous gains to patient investors.