More homes are showing up for sale this year in the Roanoke Valley — but the average cost of buying one is also rising.  Just over 2,500 realtor-listed residential units changed hands in the region between January and June, an increase of about 12% over same period last year. As for home prices: three years ago, the average sale in the region went for about $295,000, and so far this year, that number is almost $345,000. WFIR’s Evan Jones has more: