The post-tax credit slump kept Las Vegas home sales down in September, though median prices remained relatively flat from a year ago, Home Builders Research reported Tuesday. The Las Vegas-based research firm sorted through 438 new-home closings during the month, compared with 452 in September 2009. The median new-home price rose 2.2 percent to $212,870.?Existing-home sales fell to 3,540 in September, a 14.1 percent decline from 4,121 a year ago, while the median price dipped 1.8 percent to $123,000. Under normal market conditions, the gap between new and existing median home prices should be $20,000 to $30,000, Home Builders Research president Dennis Smith said. The gap began to grow in early 2009 as resale prices plummeted and is now close to $90,000.