Home sales in Southern California fell to their lowest number for a July in three years, as affordability issues and weak supply slowed the market, according to a report released Wednesday by real estate data firm DataQuick.

The median price paid for all new and existing houses and condos sold in the six-county region last month was $413,000, up more than 7 percent from the $385,000 median price a year earlier. That price is down about half a percent from the prior month.

Pricing has slowed the pace of buying considerably. Some 20,369 new and existing houses and condos were sold in the region in July, down 12.4 percent from last year and 1.4 percent since June.

Sales have fallen on a year-over-year basis for 10 consecutive months. Last month’s sales were 19.4 percent below the July average of 25,269 sales.

“Prices came a long way in a couple of years, and now a lot of would-be buyers just can’t stretch their finances enough to buy in today’s more conservative lending environment,” said CoreLogic DataQuick analyst Andrew LePage, in a statement. “That’s not the only reason price appreciation is easing, but it’s one of the main ones.”

The region includes Ventura, San Bernardino, Los Angeles, Orange, Riverside and San Diego counties.