The S&P 500 is hovering near an all-time high and has had a great year in 2017, so it's not a surprise that many stocks have delivered exceptional performance recently. However, just because a stock has risen dramatically doesn't necessarily mean it's expensive -- even if the stock has doubled in price or more. As examples, here's why our Foolish investors believe Bank of America (NYSE:BAC), SolarEdge Technologies (NASDAQ:SEDG), and Vertex Pharmaceuticals (NASDAQ:VRTX) could all still be worth a look.

Still relatively cheap with lots of potential catalysts

Matt Frankel (Bank of America): Bank of America is up 57% in 2017 alone and has gained nearly 140% since bottoming out in early 2016.

This gain has been well deserved. Not only is Bank of America's profitability getting closer and closer to where it needs to be, but the bank is also consistently profitable for the first time in years. Management has focused on investing in technology, improving efficiency, and pursuing smart risk management, and all of its efforts seem to be paying off.

Stock chart showing price rising.

Just because a stock's chart looks like this, doesn't mean it's too expensive. Image source: Getty Images.

However, there's reason to believe that Bank of America could have more room to the upside. For starters, the stock is still valued rather cheaply at 1.13 times book value, one of the lowest valuations among the larger U.S. banks, and at less than 15 times 2017's expected earnings.

In addition, there are several catalysts that could propel profits higher. With a 31% effective tax rate so far in 2017, Bank of America could keep billions more of its profits if tax reform is passed. The Federal Reserve is expected to raise interest rates several more times over the next couple of years, which should lead to margin expansion. And if Republican leaders come through on their promise to loosen banking regulations, it could translate to substantial cost savings.

SolarEdge still looks shiny

Rich Smith (SolarEdge): Solar-inverter maker SolarEdge Technologies is having a terrific November, beating earnings estimates and winning upgrades on Wall Street. In fact, with its stock up nearly 180% since the start of 2017, SolarEdge has already had a pretty terrific year -- but I think it has even more room to grow.

Last quarter, SolarEdge reported a 30% jump in revenue as solar-panel installers snapped up its inverters and solar optimizers to build into their systems. As a parts supplier, rather than a brand-name manufacturer of solar systems, SolarEdge gets to sell to everybody downstream from it -- such that its future success is tied more to the rate of solar adoption worldwide than just to the success of any one individual solar company -- not all of which are in the peak of financial health.

Analysts who follow SolarEdge see the company growing profits at 24% annualized over the next five years. That's a fast clip to be sure, but not unreasonable to expect, given that the company just finished demonstrating 30% sales growth and even faster earnings growth. What's more, at a price-to-earnings ratio of 21, SolarEdge stock looks cheap for its projected growth rate.

I don't know that SolarEdge will double again anytime soon, but this stock certainly has room to grow.

Genetically advantaged

Keith Speights (Vertex Pharmaceuticals): Vertex Pharmaceuticals stock has almost exactly doubled so far this year. The biotech stands as the undisputed leader in developing drugs for treating cystic fibrosis (CF), a genetic disease that affects more than 30,000 people in the United States. 

Kalydeco (ivacaftor) became Vertex's first CF drug to win U.S. regulatory approval in 2012 for treatment of patients with a specific gene mutation. The company's top-selling drug now, though, is Orkambi, which combined ivacaftor with another drug, lumacaftor. Orkambi is on track to generate sales of around $1.3 billion or more in 2017. Kalydeco will probably contribute close to $800 million in revenue this year. 

Success for these two drugs has definitely made Vertex attractive to investors, but the stock's momentum in 2017 has resulted even more from the biotech's pipeline. In March, Vertex announced positive results from a couple of late-stage studies evaluating a combination of tezecaftor and ivacaftor in treating CF. An approval decision from the FDA is expected by Feb. 28. The biotech followed up a few months later with solid results from phase 1 and phase 2 studies of three different triple-combination CF therapies.

Vertex's management wants to become to CF what Gilead Sciences (NASDAQ: GILD) is in the HIV market. I think the biotech just might achieve that goal. This stock still has plenty of room to run.

Keith Speights has no position in any of the stocks mentioned. Matthew Frankel owns shares of Bank of America. Rich Smith owns shares of SolarEdge Technologies. The Motley Fool recommends Vertex Pharmaceuticals. The Motley Fool has a disclosure policy.