If industry insiders laughed at the $450 million Joe Lacob and Peter Guber paid for the Golden State Warriors in November 2010, one has to wonder what they would think now.

Less than three years after the two agreed to pay the highest price ever for an NBA franchise, the team is now valued at $800 million, according to a source with knowledge of the terms.

The new valuation comes from the price Silicon Valley venture capitalist Mark Stevens agreed to pay for a share of the team that was made available when former partner Vivek Ranadive had to sell it to buy the Sacramento Kings in May.

In a way, Ranadive's agreement to pay about $550 million for 72 percent of the Kings and their existing arena helped his old partners sell their stake for even more. The $800 million number is still surprising, given that Forbes magazine valued the Warriors in January at $555 million. Warriors spokesman Raymond Ridder declined to comment on the new valuation or the percentage that Stevens bought.

Stevens, the managing partner of S-Cubed Capital in Menlo Park, Calif., was presumably not only paying for the present, but also for the future. Last year, the team announced its intention to build a privately funded arena in San Francisco, which is still going through the necessary approvals. If all goes well, the ownership group hopes to have it open in time for the 2017-18 season.

The Warriors are coming off their best regular-season record (47-35) since the 2007-08 season and the most successful playoff run since 1977, when they took the San Antonio Spurs to six games in the Western Conference semifinals.

In the offseason, the Warriors completed a sign-and-trade for Andre Iguodala to join Stephen Curry, Klay Thompson and David Lee, an acquisition that helped at the box office.

The team, which sold out 38 consecutive games last season, sold more than 3,000 new season tickets this summer to grow the season-ticket base to an all-time high of nearly 14,000. With president Rick Welts, adviser Jerry West and former agent Bob Myers as general manager, the team has assembled one of the more impressive front offices in the NBA to support its up-and-coming coach, Mark Jackson.