The group that reached a purchase agreement last month to buy the Sacramento Kings took the next step in bringing the National Basketball Association back to Seattle by filing to relocate the team. NBA Commissioner David Stern told reporters last night that the “very strong” group, headed by Valiant Capital Management founder Chris Hansen and including Microsoft Corp. Chief Executive Officer Steve Ballmer, submitted a relocation proposal in which the team would play at KeyArena in Seattle for two or three seasons while a new facility is built. Seattle has been without an NBA team since 2008, when the SuperSonics ended their 41-year stay by moving to Oklahoma City and becoming the Thunder. That move followed a lack of public support for a new venue to replace KeyArena, where the Sonics played since their inception in 1967. The prospective ownership group had to apply to the league for relocation by March 1 to play in Seattle next season. That request, as well as the sale agreement, would have to be approved by the NBA’s board of governors, which is made up of league owners. Hansen’s group reached an agreement on Jan. 21 with the Maloof family, which has owned the Kings since 1999, that puts the team’s value at $525 million. It would be the highest sale price for an NBA team, surpassing the $450 million paid for the Golden State Warriors in 2010.