“I think there is in the V.C. community a sense that the rules have changed or are changing,” said John Battelle, a journalist and entrepreneur, who is a host of a technology conference in San Francisco this week that will include a panel on the subject. “How does the V.C. who is set up for a model that requires millions, if not tens of millions, revamp for a different scale?”

And as large firms try to go small, they are encountering a new crop of competitors who are happy to bankroll start-ups on the cheap and are fueling the current Internet boom. They include a large pool of angel investors and a number of small venture funds whose specialty is to invest tens of thousands of dollars, or hundreds of thousands at most.

There is even a group called Y Combinator, whose rule of thumb for investing in start-ups is $6,000 per employee. One of its investments, Reddit, was acquired last week by Wired Digital, which is owned by Condé Nast Publications, for an undisclosed sum.

“I came to the conclusion that $500,000 was the new $5 million,” said Michael Maples Jr., an entrepreneur who created a $15 million venture fund aimed at investing in companies that required little capital. Mr. Maples sees himself not so much as a competitor to venture capitalists, but as someone who is filling the gap between angels, who may invest $250,000 or so in a start-up, and venture investors, whose typical early-stage bet is closer to $5 million.

Several forces are allowing companies to operate cheaply compared with the first Internet boom. They include the declining costs of hardware and bandwidth, the wide availability of open-source software, and the ability to generate revenue through online ads.

“It’s a great time to be an entrepreneur,” Joe Kraus, a veteran of the dot-com boom, wrote in a widely noted blog posting last year. Mr. Kraus said it took $3 million to get his first start-up, Excite.com, from idea to product, much of it spent on servers and software, which have since become much cheaper or even free. His new start-up, JotSpot, was started on just $100,000.

With the notable exception of YouTube, many recent acquisitions involved Internet start-ups that simply could not effectively use large amounts from venture capitalists or produce large returns, said Paul Kedrosky, a venture capitalist and blogger.