High growth at a reasonable price is hard to come by in this market. But that’s the deal we think eBay (NSDQ: EBAY) stock is offering investors now.

Last year, earnings were up 16 percent on a 21 percent rise in revenue. And the consensus among analysts is for earnings to keep climbing at least this fast through 2015.

What’s behind this surge? EBay is aggressively expanding into two high-growth/high-competition sectors: (1) online retail; and (2) electronic payments, both online and in regular stores. If successful in gaining market share in these sectors, eBay will be on a new growth trajectory.

Online marketplace (54 percent of revenue). EBay.com is still known as an auction website that matches buyers with sellers. But 70 percent of what’s sold on eBay sites today is at fixed prices, through the “Buy It Now” option. So increasingly, eBay’s marketplace is looking more like that of Amazon.com (NSDQ: AMZN), including the emphasis on foreign markets, which bring in more than 50 percent of eBay’s revenue.

To compete with Amazon, eBay revamped its website and added personalized home pages for users based on their buying preferences. To attract sellers, it updated its listing fees and is highlighting the fact that it’s a partner to vendors, unlike Amazon, which has its own products to sell. Also in 2012, the firm launched “eBay Now” in San Francisco and New York City, allowing consumers to buy from local retailers and get delivery in as little as an hour.

These efforts are starting to pay off. In the first quarter of 2013, eBay.com added 3.9 million new active users, up 13 percent. The goal is for marketplace revenue to hit $11 billion by 2015, up close to 40 percent.

PayPal (40 percent of revenue). Bought by eBay in 2002, PayPal is the payment method now used for about 25 percent of all US online sales, including purchases via cell phone. Yet eBay has even higher ambitions. It’s expanding into offline sales, a market 10 times larger, and thus hoping to boost PayPal revenue 40 percent by 2015.

PayPal’s partnership with credit-card issuer Discover (NYSE: DFS), which begins this quarter, will make major headway toward this, by allowing shoppers with PayPal accounts to pay using only their cell phone number and PIN.

By the end of 2013, payment via PayPal will be possible at more than 2 million US merchants, including 23 major retailers such as Home Depot and Toys R Us.

Google’s (NSDQ: GOOG) payment system (“Wallet” and “Checkout”) and a service called “Square,” could turn out to be fierce competitors. But currently they’re lagging PayPal, which has the first-mover advantage.

GSI Commerce (6 percent of revenue). Acquired in 2011, GSI helps large retailers and brands develop and operate their online marketplaces. While not a big part of eBay’s revenue, GSI is a key to getting offline merchants comfortable with using PayPal.

Recently around $52, eBay stock is up about 30 percent in the past year. But we think the shares are still reasonably priced, at 19 times 2013 earnings estimates. Consider that investors are willing to pay 82 times 2013 estimated earnings for Amazon.com, 23 times for VISA (NYSE: V) and 21 times for MasterCard (NYSE: MA).

EBay also has a lot of excess cash, $11.5 billion (3 times its debt) that it can use to expand, buy back stock or declare a dividend.

Hitting the “Buy It Now” button for eBay stock is likely to be a winning move.